dsPIC33/PIC24 Family Reference Manual, UART

 2009-2013 Microchip Technology Inc. DS70000582E-page 1

HIGHLIGHTS

This section of the manual contains the following major topics:

1.0 Introduction ....................................................................................................................... 2

2.0 Control Registers .............................................................................................................. 4

3.0 UART Baud Rate Generator ........................................................................................... 12

4.0 UART Configuration........................................................................................................ 14

5.0 UART Transmitter ........................................................................................................... 15

6.0 Data Bit Detection ...........................................................................................................20

7.0 UART Receiver ............................................................................................................... 21

8.0 Using the UART for 9-Bit Communication ...................................................................... 26

9.0 Other Features of the UART ........................................................................................... 29

10.0 UART Operation with DMA ............................................................................................. 31

11.0 UART Operation During CPU Sleep and Idle Modes ..................................................... 33

12.0 Operation of UxCTS and UxRTS Control Pins ............................................................... 35

13.0 Infrared Support .............................................................................................................. 37

14.0 LIN/J2602 Support.......................................................................................................... 40

15.0 Smart Card Support........................................................................................................ 42

16.0 Registers Map................................................................................................................. 51

17.0 Related Application Notes............................................................................................... 52

18.0 Revision History .............................................................................................................. 53

Universal Asynchronous Receiver Transmitter (UART)

dsPIC33/PIC24 Family Reference Manual

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This document supersedes the following PIC24 and dsPIC Family Reference Manual sections:

1.0 INTRODUCTION

The Universal Asynchronous Receiver Transmitter (UART) module is one of the serial I/O

modules available in the dsPIC33 and PIC24 device families. The UART is a full-duplex,

asynchronous communication channel that communicates with peripheral devices and personal

computers, using protocols such as RS-232, RS-485, LIN/J2602 and IrDA

. The module also

supports the hardware flow control option with the UxCTS

and UxRTS pins and includes the IrDA

encoder and decoder.

The primary features of the UART module are as follows:

• Full-duplex, 8-bit or 9-bit data transmission through the UxTX and UxRX pins

• Even, odd or no parity options (for 8-bit data)

• One or two Stop bits

• Hardware auto-baud feature

• Hardware flow control option with the UxCTS

and UxRTS pins (These pins are not

available on all devices. Refer to the “Universal Asynchronous Receiver Transmitter

(UART)” chapter of the specific device data sheet for availability.)

• Fully integrated Baud Rate Generator (BRG) with 16-bit prescaler

• Baud rates up to 17.5 Mbps

• Four-deep First-In First-Out (FIFO) transmit data buffer

• Four-deep FIFO receive data buffer

• Parity, framing and buffer overrun error detection

• Support for 9-bit mode with address detect (9th bit = 1)

• Transmit and receive interrupts

• Loopback mode for diagnostic support

• IrDA encoder and decoder logic

• LIN/J2602 bus support (v1.3 and 2.0)

• 16x baud clock output for external IrDA encoder/decoder support

• Optional ISO 7816 Smart Card support

Note: This family reference manual section is meant to serve as a complement to device

data sheets. Depending on the device variant, this manual section may not apply to

all dsPIC33 and PIC24 devices.

Please consult the note at the beginning of the “Universal Asynchronous

Receiver Transmitter (UART)” chapter in the current device data sheet to check

whether this document supports the device you are using.

Device data sheets and family reference manual sections are available for download

from the Microchip worldwide web site at: http://www.microchip.com

DS Number Section Number Title

DS39708 21 UART: PIC24F Family Reference Manual

DS70232 17 UART: PIC24H Family Reference Manual

DS70582 17 UART: dsPIC33E/PIC24E Family Reference Manual

DS70066 19, 34 UART: dsPIC30F Family Reference Manual

DS70188 17 UART: dsPIC33F/PIC24H Family Reference Manual

DS70582 17 UART: dsPIC33E/PIC24E Family Reference Manual

 2009-2013 Microchip Technology Inc. DS70000582E-page 3

UART

A simplified block diagram of the UART is illustrated in Figure 1-1. The UART module consists

of the following key hardware elements:

• Baud Rate Generator

• Asynchronous Transmitter

• Asynchronous Receiver

Figure 1-1: UARTx Simplified Block Diagram

Baud Rate Generator

UxRX

Hardware Flow Control

UARTx Receiver

UARTx Transmitter

UxTX

UxCTS

UxRTS

BCLKx

ISO 7816 Support

IrDA

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2.0 CONTROL REGISTERS

This section outlines the specific functions of each register that controls the operation of the

UART module:

• UxMODE: UARTx Mode Register

- Enables or disables the UART module

- Enables or disables the IrDA encoder and decoder

- Enables or disables the WAKE, ABAUD bits and Loopback features

- Enables or disables the UxRTS

and UxCTS pins

- Configures the UxRTS pin for the desired mode of operation

- Configures the polarity of the UxRX pin

- Selects the type of baud rate

- Selects the number of data bits, parity and Stop bits

• UxSTA: UARTx Status and Control Register

- Selects the Transmission Interrupt mode

- Selects the Receive Interrupt mode

- Enables or disables the UART transmission

- Controls the Address Detect mode

- Indicates various status conditions, such as transmit and receive buffer state, parity

error, framing error and overflow error

• UxADMD: UARTx Address Mask Detect Register

- Stores address match and mask values

• UxRXREG: UARTx Receive Register

- Stores the received data

• UxTXREG: UARTx Transmit Register (Write-Only)

- Provides the data to be transmitted

• UxBRG: UARTx Baud Rate Register

- Stores the baud rate value of the transmitted or received data

Note: Each dsPIC33/PIC24 family device variant may have one or more UART modules.

An ‘x’ used in the names of pins, control/status bits and registers denotes the par-

ticular UART module number. Refer to the “Universal Asynchronous Receiver

Transmitter (UART)” chapter of the specific device data sheet for more details.

 2009-2013 Microchip Technology Inc. DS70000582E-page 5

UART

R/W-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

UARTEN

(3)

— USIDL IREN

(1)

RTSMD ALTIO

(2)

UEN1

(2)

UEN0

(2)

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

WAKE

(4)

LPBACK ABAUD

(5)

URXINV BRGH PDSEL1 PDSEL0 STSEL

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15 UARTEN: UARTx Enable bit

(3)

1 = UARTx is enabled; UARTx pins are controlled by UARTx as defined by the UEN<1:0> and

UTXEN control bits

0 = UARTx is disabled; UARTx pins are controlled by the corresponding PORTx, LATx and TRISx bits

bit 14 Unimplemented: Read as ‘0’

bit 13 USIDL: UARTx Stop in Idle Mode bit

1 = Discontinues operation when the device enters Idle mode

0 = Continues operation in Idle mode

bit 12 IREN: IrDA

Encoder and Decoder Enable bit

(1)

1 = IrDA encoder and decoder are enabled

0 = IrDA encoder and decoder are disabled

bit 11 RTSMD: Mode Selection for UxRTS

Pin bit

1 = UxRTS is in Simplex mode

0 = UxRTS

is in Flow Control mode

bit 10 ALTIO: UARTx Alternate I/O Selection bit

(2)

1 = UARTx communicates using UxATX and UxARX I/O pins

0 = UARTx communicates using UxTX and UxRX I/O pins

bit 9-8 UEN<1:0>: UARTx Enable bits

(2)

11 = UxTX, UxRX and BCLKx pins are enabled and used; UxCTS pin is controlled by port latches

10 = UxTX, UxRX, UxCTS

and UxRTS pins are enabled and used

01 = UxTX, UxRX and UxRTS

pins are enabled and used; UxCTS pin is controlled by port latches

00 = UxTX and UxRX pins are enabled and used; UxCTS

, UxRTS and BCLKx pins are controlled by

port latches

bit 7 WAKE: Enable Wake-up on Start bit Detect During Sleep Mode bit

(4)

1 = Wake-up is enabled

0 = Wake-up is disabled

bit 6 LPBACK: UARTx Loopback Mode Select bit

1 = Enables Loopback mode

0 = Loopback mode is disabled

Note 1: This feature is only available for Standard Speed mode (BRGH = 0). Refer to the “Universal Asynchronous

Receiver Transmitter (UART)” chapter of the specific device data sheet for availability.

2: These features may not be available on all devices. Refer to the “Universal Asynchronous Receiver

Transmitter (UART)” chapter of the specific device data sheet for availability.

3: Enable this bit before enabling the UTXEN bit (UxSTA<10>).

4: The UARTx module does not recognize the first character received on a wake.

5: The use of this feature may consume the corresponding Input Capture x (ICx) peripheral. See Section 9.2

“Auto-Baud Support” for more information.

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bit 5 ABAUD: Auto-Baud Enable bit

(5)

1 = Enables baud rate measurement on the next character, requires reception of a Sync field (0x55);

cleared in hardware upon completion

0 = Baud rate measurement is disabled or complete

bit 4 URXINV: UARTx Receive Polarity Inversion bit

1 = UxRX Idle state is ‘0’

0 = UxRX Idle state is ‘1’

bit 3 BRGH: High Baud Rate Select bit

1 = BRG generates 4 clocks per bit period (4x baud clock, High-Speed mode)

0 = BRG generates 16 clocks per bit period (16x baud clock, Standard Speed mode)

bit 2-1 PDSEL<1:0>: Parity and Data Selection bits

11 = 9-bit data, no parity

10 = 8-bit data, odd parity

01 = 8-bit data, even parity

00 = 8-bit data, no parity

bit 0 STSEL: Stop Selection bit

1 = 2 Stop bits

0 = 1 Stop bit

Note 1: This feature is only available for Standard Speed mode (BRGH = 0). Refer to the “Universal Asynchronous

Receiver Transmitter (UART)” chapter of the specific device data sheet for availability.

2: These features may not be available on all devices. Refer to the “Universal Asynchronous Receiver

Transmitter (UART)” chapter of the specific device data sheet for availability.

3: Enable this bit before enabling the UTXEN bit (UxSTA<10>).

4: The UARTx module does not recognize the first character received on a wake.

5: The use of this feature may consume the corresponding Input Capture x (ICx) peripheral. See Section 9.2

“Auto-Baud Support” for more information.

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UART

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R-0 R-1

UTXISEL1 UTXINV UTXISEL0 URXEN

(1)

UTXBRK UTXEN

(2)

UTXBF TRMT

(3)

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R-1 R-0 R-0 R/C-0 R-0

URXISEL1 URXISEL0 ADDEN RIDLE PERR FERR OERR URXDA

bit 7 bit 0

Legend: C = Clearable bit

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15,13 UTXISEL<1:0>: UARTx Transmission Interrupt Mode Selection bits

11 = Reserved

10 = Interrupt is generated when a character is transferred to the Transmit Shift Register (TSR) and

the transmit buffer becomes empty

01 = Interrupt is generated when the last transmission is over, transmit buffer is empty (i.e., the last

character has been shifted out of the Transmit Shift Register) and all the transmit operations are

completed

00 = Interrupt is generated when any character is transferred to the Transmit Shift Register and the

transmit buffer is empty (which implies at least one location is empty in the transmit buffer)

bit 14 UTXINV: UARTx Transmit Polarity Inversion bit

IREN =

1 = UxTX Idle state is ‘0’

0 = UxTX Idle state is ‘1’

IREN = 1:

1 = IrDA

is encoded, UxTX Idle state is ‘1’

0 = IrDA is encoded, UxTX Idle state is ‘0’

bit 12 URXEN: UARTx Receive Enable bit

(1)

1 = Receive is enabled, UxRX pin is controlled by UARTx

0 = Receive is disabled, UxRX pin is controlled by the port

bit 11 UTXBRK: UARTx Transmit Break bit

1 = UxTX pin is driven low regardless of the transmitter state (Sync Break transmission – Start bit is

followed by twelve ‘0’s and a Stop bit)

0 = Sync Break transmission is disabled or complete

bit 10 UTXEN: UARTx Transmit Enable bit

(2)

1 = UARTx transmitter is enabled; UxTX pin is controlled by UARTx (if UARTEN = 1)

0 = UARTx transmitter is disabled; any pending transmission is aborted and the buffer is reset, UxTX

pin is controlled by the port

bit 9 UTXBF: UARTx Transmit Buffer Full Status bit (read-only)

1 = Transmit buffer is full

0 = Transmit buffer is not full; at least one more data word can be written

bit 8 TRMT: Transmit Shift Register is Empty bit (read-only)

(3)

1 = Transmit Shift Register is empty and the transmit buffer is empty (i.e., the last transmission has

completed)

0 = Transmit Shift Register is not empty; a transmission is in progress or queued in the transmit buffer

Note 1: This bit is only available in devices supporting Smart Card. Refer to the “Universal Asynchronous

Receiver Transmitter (UART)” chapter of the specific device data sheet for availability.

2: Enable the UARTEN bit (UxMODE<15>) before enabling this bit.

3: User software should wait at least one instruction cycle between writing UxTXREG and reading the TRMT bit.

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bit 7-6 URXISEL<1:0>: UARTx Receive Interrupt Mode Selection bits

11 = Interrupt flag bit is set when the receive buffer is full (i.e., 4 data characters)

10 = Interrupt flag bit is set when the receive buffer is 3/4 full (i.e., 3 data characters)

0x = Interrupt flag bit is set when a character is received

bit 5 ADDEN: Address Character Detect bit (bit 8 of received data = 1)

1 = Address Detect mode is enabled; if 9-bit mode is not selected, this control bit has no effect

0 = Address Detect mode is disabled

bit 4 RIDLE: Receiver Idle bit (read-only)

1 = Receiver is Idle

0 = Data is being received

bit 3 PERR: Parity Error Status bit (read-only)

1 = Parity error has been detected for the current character

0 = Parity error has not been detected

bit 2 FERR: Framing Error Status bit (read-only)

1 = Framing error has been detected for the current character

0 = Framing error has not been detected

bit 1 OERR: Receive Buffer Overrun Error Status bit (clear/read-only)

1 = Receive buffer has overflowed

0 = Receive buffer has not overflowed (clearing a previously set OERR bit will reset the receive buffer

and RSR to an empty state)

bit 0 URXDA: UARTx Receive Buffer Data Available bit (read-only)

1 = Receive buffer has data; at least one more character can be read

0 = Receive buffer is empty

Note 1: This bit is only available in devices supporting Smart Card. Refer to the “Universal Asynchronous

Receiver Transmitter (UART)” chapter of the specific device data sheet for availability.

2: Enable the UARTEN bit (UxMODE<15>) before enabling this bit.

3: User software should wait at least one instruction cycle between writing UxTXREG and reading the TRMT bit.

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UART

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

ADM_MASK<7:0>

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

ADM_ADDR<7:0>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-8 ADM_MASK<7:0>: Address Mask bits

Used to mask the ADM_ADDR<7:0> bits.

For ADM_MASK<n>:

1 = ADM_ADDR<n> is used to detect the address match

0 = ADM_ADDR<n> is not used to detect the address match

bit 7-0 ADM_ADDR<7:0>: Address Detect Task Off-Load bits

Used with ADM_MASK<7:0> to off-load the task of detecting the address character from the processor

during Address Detect mode.

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U-0 U-0 U-0 U-0 U-0 U-0 U-0 R-0

— — — — — — — URX8

bit 15 bit 8

R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0

URX<7:0>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-9 Unimplemented: Read as ‘0’

bit 8 URX8: Data bit 8 of the Received Character (in 9-bit mode)

bit 7-0 URX<7:0>: Data bits 7-0 of the Received Character

W-x U-0 U-0 U-0 U-0 U-0 U-0 W-x

LAST

(1)

— — — — — —UTX8

bit 15 bit 8

W-x W-x W-x W-x W-x W-x W-x W-x

UTX<7:0>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15 LAST: Last Byte Indicator for Smart Card Support bit

(1)

bit 14-9 Unimplemented: Read as ‘0’

bit 8 UTX8: Data bit 8 of the Transmitted Character (in 9-bit mode)

bit 7-0 UTX<7:0>: Data bits 7-0 of the Transmitted Character

Note 1: This bit is only available in devices supporting Smart Card. Refer to the “Universal Asynchronous

Receiver Transmitter (UART)” chapter of the specific device data sheet for availability.

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UART

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

BRG<15:8>

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

BRG<7:0>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-0 BRG<15:0>: Baud Rate Divisor bits

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3.0 UART BAUD RATE GENERATOR

The UART module consists of a dedicated 16-bit Baud Rate Generator. The UxBRG register

controls the period of a free-running, 16-bit timer. Equation 3-1 shows the formula for computing

the baud rate with BRGH = 0.

Equation 3-1: UARTx Baud Rate (BRGH = 0)

Equation 3-2 shows the calculation of baud rate error for the following conditions:

•F

P = 4 MHz

• Desired Baud Rate = 9600

Equation 3-2: Baud Rate Error Calculation (BRGH = 0)

The maximum baud rate (BRGH = 0) possible is F

P/16 (for UxBRG = 0) and the minimum baud

rate possible is F

P/(16 * 65536).

Equation 3-3 shows the formula for computing the baud rate with BRGH = 1.

Equation 3-3: UARTx Baud Rate (BRGH = 1)

The maximum baud rate (BRGH = 1) possible is F

P/4 (for UxBRG = 0) and the minimum baud

rate possible is F

P/(4 * 65536).

Writing a new value to the UxBRG register causes the BRG timer to reset (cleared). This ensures

the BRG does not wait for a timer overflow before generating the new baud rate.

Note: FP denotes the instruction cycle clock frequency (FOSC/2).

Baud Rate

16 UxBRG 1+

----------------------------------------------=

UxBRG

16 Baud Rate

-------------------------------------1–=

...... (1)

...... (2)

Desired Baud Rate

16 UxBRG 1+

----------------------------------------------=

Solving for UxBRG Value:

UxBRG

P Desired Baud Rate

-------------------------------------------------------- 1–=

Calculated Baud Rate

4000000

16 25 1+

--------------------------------=

Error

Calculated Baud Rate Desired Baud Rate–

Desired Baud Rate

--------------------------------------------------------------------------------------------------------=

9615 9600–

9600

----------------------------- -=

0.16%=

4000000 9600

------------------------------------ -1–





25=

...... (1)

...... (2)

9615=

Note: FP denotes the instruction cycle clock frequency.

Baud Rate

4 UxBRG 1+

-------------------------------------------=

UxBRG

4 Baud Rate

---------------------------------- 1–=

...... (1)

...... (2)

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UART

3.1 BCLKx Output

The BCLKx pin outputs the 16x baud clock if the UART and BCLKx output are enabled

(UEN<1:0> = 11). This feature is used for external IrDA encoder/decoder support (see Figure 3-1).

The BCLKx output stays high during Sleep mode. BCLKx is forced as an output as long as the

UART is kept in this mode (UEN<1:0> = 11), regardless of the PORTx and TRISx latch bits.

Figure 3-1: BCLKx Output vs. UxBRG Programming

(N + 1)TP

BCLKx @ BRG = 0

BCLKx @ BRG = 1

BCLKx @ BRG = 2

BCLKx @ BRG = 3

BCLKx @ BRG = 4

BCLKx @ BRG = N

UxTX

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4.0 UART CONFIGURATION

The UART uses the standard Non-Return-to-Zero (NRZ) format (one Start bit, eight or nine Data

bits and one or two Stop bits). Parity is supported by the hardware and can be configured by the

user application as even, odd or no parity. The most common data format is eight bits, no parity

and one Stop bit (denoted as 8, N, 1), which is the default (POR) setting. The number of data

bits, Stop bits and the parity are specified in the PDSEL<1:0> (UxMODE<2:1>) and STSEL

(UxMODE<0>) bits. An on-chip, dedicated, 16-bit Baud Rate Generator can be used to derive

standard baud rate frequencies from the oscillator. The UART transmits and receives the Least

Significant bit (LSb) first. The transmitter and receiver of the UART module are functionally

independent, but use the same data format and baud rate.

4.1 Enabling the UART

The UART module is enabled by setting the UARTEN (UxMODE<15>) and UTXEN

(UxSTA<10>) bits. Once enabled, the UxTX pin is configured as an output and the UxRX pin as

an input, overriding the TRISx and PORTx register bit settings for the corresponding I/O port

pins. The UxTX pin is at logic ‘1’ when no transmission is taking place.

4.2 Disabling the UART

The UART module is disabled by clearing the UARTEN bit (UxMODE<15>). This is the default

state after any Reset. If the UART is disabled, all UART pins operate as port pins under the

control of their corresponding PORTx and TRISx bits.

Disabling the UART module resets the buffers to empty states. Any data characters in the buffers

are lost and the baud rate counter is reset.

All error and status flags associated with the UART module are reset when the module is

disabled. The UTXBRK, UTXEN, UTXBF, PERR, FERR, OERR and URXDA bits are cleared,

whereas the TRMT and RIDLE bits are set. Other control bits (including ADDEN, URXISEL<1:0>

and UTXISEL<1:0>), and the UxMODE and UxBRG registers are not affected.

The clearing of the UARTEN bit while the UART is active will abort all pending transmissions and

receptions, and resets the module as defined above. Re-enabling the UART will restart the UART

in the same configuration.

Note: The UTXEN bit is set after the UARTEN bit has been set; otherwise, UART

transmissions will not be enabled.

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UART

5.0 UART TRANSMITTER

The transmitter block diagram of the UART module is illustrated in Figure 5-1. The important part

of the transmitter is the UARTx Transmit Shift Register (UxTSR). The Shift register obtains its

data from the transmit FIFO buffer, UxTXREG. The UxTXREG register is loaded with data in soft-

ware. The UxTSR register is not loaded until the Stop bit has been transmitted from the previous

load. As soon as the Stop bit is transmitted, the UxTSR is loaded with new data from the

UxTXREG register (if available).

Figure 5-1: UARTx Transmitter Block Diagram

The transmission is enabled by setting the UTXEN enable bit (UxSTA<10>). The actual trans-

mission will not occur until the UxTXREG register has been loaded with data and the Baud Rate

Generator (UxBRG) has produced a shift clock (Figure 5-1). Normally, when the first transmis-

sion is started, the UxTSR register is empty, so a transfer to the UxTXREG register will result in

an immediate transfer to UxTSR. Clearing the UTXEN bit during a transmission will cause the

transmission to be aborted and will reset the transmitter. As a result, the UxTX pin will revert to

a high-impedance state.

To select 9-bit transmission, the PDSEL<1:0> bits (UxMODE<2:1>) should be set to ‘11’ and the

ninth bit should be written to the UTX8 bit (UxTXREG<8>). A word write should be performed to

UxTXREG, so that all nine bits are written at the same time.

Note: The UxTSR register is not mapped in data memory, so it is not available to the user

application.

Word Write-Only

Word or

UTX8 UxTXREG Low Byte

Load UxTSR

Transmit Control

– Control UxTSR

– Control Buffer

– Generate Flags

– Generate Interrupt

UxTXIF

Data

(Start)

(Stop)

Parity

Generator

Transmit Shift Register (UxTSR)

Control

Signals

16x Baud Clock

from Baud Rate

Generator

Internal Data Bus

UTXBRK

Note: ‘x’ denotes the UART number.

UxTX

UxMODE

UxSTA

Byte Write

Transmit FIFO

15 9 8 7 0

UxCTS

UTXINV

 16 Divider

Note: There is no parity in case of a 9-bit data transmission.

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On a device Reset, the UxTX pin is configured as an input; therefore, the state of the UxTX pin

is undefined. When the UART module is enabled, the transmit pin is driven high. It remains in

this state until data is written to the transmit buffer (UxTXREG). The transmit pin is driven low as

soon as the first data is written to the UxTXREG register. To ensure the Start bit detection, it is

recommended to have a delay between enabling the UARTx (UARTEN = 1) and initiating the first

transmission. The delay is baud rate dependent and should be equal to, or longer than, the time

it takes to transmit one data bit.

Figure 5-2: UARTx Transmission

5.1 Transmit Buffer (UxTXREG)

The transmit buffer is 9 bits wide and 4 levels deep. Along with the UARTx Transmit Shift Register

(UxTSR), the user effectively has a 5-level deep buffer. It is organized as a First-In First-Out

(FIFO). Once the UxTXREG contents are transferred to the UxTSR register, the current buffer

location becomes available for new data to be written and the next buffer location is sourced to

the UxTSR register. The UTXBF (UxSTA<9>) status bit is set whenever the buffer is full. If a user

application attempts to write to a full buffer, the new data will not be accepted into the FIFO.

The FIFO is reset during any device Reset, but is not affected when the device enters a power-saving

mode or wakes up from a power-saving mode.

5.2 Transmit Interrupt

The UARTx Transmit Interrupt Flag bit (UxTXIF) is located in the corresponding Interrupt Flag

Status (IFS) register. The UTXISEL<1:0> control bits (UxSTA<15,13>) determine when the

UART will generate a transmit interrupt.

• If UTXISEL<1:0> = 00, the UxTXIF bit is set when a character is transferred from the

transmit buffer to the UARTx Transmit Shift Register (UxTSR) or the transmit buffer is

empty. This implies at least one location is empty in the transmit buffer.

• If UTXISEL<1:0> = 01, the UxTXIF bit is set when the last character is shifted out of the

UxTSR register. This implies that all the transmit operations are completed.

• If UTXISEL<1:0> = 10, the UxTXIF bit is set when the character is transferred to the

UxTSR register and the transmit buffer is empty.

The UxTXIF bit is set when the module is first enabled. The user application should clear the

UxTXIF bit in the Interrupt Service Routine (ISR).

Switching between the two interrupt modes during operation is possible.

While the UxTXIF flag bit indicates the status of the UxTXREG register, the TRMT bit

(UxSTA<8>) indicates the status of the UxTSR. The TRMT status bit is a read-only bit, which is

set when the UxTSR is empty. No interrupt logic is tied to this bit, so the user application has to

poll this bit to determine if the UxTSR is empty.

Note: When the UTXEN bit is set, the UxTXIF flag bit will also be set regardless of the

UTXISEL bits (UxSTA<15,13>) settings.

UxTX

1 2

B0 B1 B2 B3 B4 B5 B6 B7

Bit Time = T

Software

Delay

1. The UARTx module is enabled (UARTEN = 1).

2. Data is written to the transmit buffer (UxTXREG) to begin the transmission.

 2009-2013 Microchip Technology Inc. DS70000582E-page 17

UART

5.3 Setup for UART Transmit

The following steps are used to set up a transmission:

1. Initialize the UxBRG register for the appropriate baud rate (see Section 3.0 “UART Baud

Rate Generator”).

2. Set the number of data bits, number of Stop bits and parity selection by writing to the

PDSEL<1:0> (UxMODE<2:1>) and STSEL (UxMODE<0>) bits.

3. If transmit interrupts are desired, set the UxTXIE control bit in the corresponding Interrupt

Enable Control x register (IECx).

4. Specify the interrupt priority for the transmit interrupt using the UxTXIP<2:0> control bits in

the corresponding Interrupt Priority Control x register (IPCx). Also, select the Transmit

Interrupt mode by writing to the UTXISEL<1:0> bits (UxSTA<15,13>).

5. Enable the UART module by setting the UARTEN bit (UxMODE<15>).

6. Enable the transmission by setting the UTXEN bit (UxSTA<10>), which also sets the UxTXIF bit.

7. The UxTXIF bit should be cleared in the software routine that services the UART transmit

interrupt. The operation of the UxTXIF bit is controlled by the UTXISEL<1:0> control bits.

8. Load data into the UxTXREG register (starts transmission).

If 9-bit transmission has been selected, load a word. If 8-bit transmission is used, load a

byte. Data can be loaded into the buffer until the UTXBF status bit (UxSTA<9>) is set.

Example 5-1 provides the sample code that sets up the UART for transmission.

Figure 5-3: UARTx Transmission (8-Bit or 9-Bit Data)

Figure 5-4: UARTx Transmission (Back-to-Back)

Note: The UTXEN bit should not be set until the UARTEN bit has been set; otherwise,

UART transmissions will not be enabled. Writing data to the UxTXREG should be

done after the UTXEN bit is set.

Character 1

Stop bit

Character 1 to

Transmit Shift Register

Start bit bit 0 bit 1 bit 7/8

Write to UxTXREG

BCLKx/16

(Shift Clock)

UxTX

UxTXIF

TRMT bit

Character 1

UxTXIF Cleared by User in Software

Transmit Shift Register

Write to UxTXREG

BCLKx/16

(Shift Clock)

UxTX

UxTXIF

TRMT bit

Character 1 Character 2

Character 1 to Character 2 to

Start bit Stop bit Start bit

Transmit Shift Register

Character 1 Character 2

bit 0 bit 1 bit 7/8 bit 0

Note: This timing diagram shows two consecutive transmissions.

(UTXISEL<1:0> =

)

UxTXIF

(UTXISEL<1:0> =

)

UxTXIF Cleared by User in Software

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DS70000582E-page 18  2009-2013 Microchip Technology Inc.

Example 5-1: UART1 Transmission with Interrupts

#define FP 40000000

#define BAUDRATE 9600

#define BRGVAL ((FP/BAUDRATE)/16)-1

unsigned int i;

#define DELAY_105uS asm volatile ("REPEAT, #4201"); Nop(); // 105uS delay

int main(void)

{

// Configure oscillator as needed

U1MODEbits.STSEL = 0; // 1-Stop bit

U1MODEbits.PDSEL = 0; // No Parity, 8-Data bits

U1MODEbits.ABAUD = 0; // Auto-Baud disabled

U1MODEbits.BRGH = 0; // Standard-Speed mode

U1BRG = BRGVAL; // Baud Rate setting for 9600

U1STAbits.UTXISEL0 = 0; // Interrupt after one TX character is transmitted

U1STAbits.UTXISEL1 = 0;

IEC0bits.U1TXIE = 1; // Enable UART TX interrupt

U1MODEbits.UARTEN = 1; // Enable UART

U1STAbits.UTXEN = 1; // Enable UART TX

/* Wait at least 105 microseconds (1/9600) before sending first char */

DELAY_105uS

U1TXREG = 'a'; // Transmit one character

while(1)

{

}

void __attribute__((__interrupt__)) _U1TXInterrupt(void)

{

IFS0bits.U1TXIF = 0; // Clear TX Interrupt flag

U1TXREG = 'a'; // Transmit one character

}

 2009-2013 Microchip Technology Inc. DS70000582E-page 19

UART

5.4 Transmission of Break Characters

A Break character transmit consists of a Start bit, followed by twelve bits of ‘0’ and a Stop bit. A

Frame Break character is sent whenever the UTXBRK and UTXEN bits are set, while the

Transmit Shift Register is loaded with data. A dummy write to the UxTXREG register is necessary

to initiate the Break character transmission. Note that the data value written to the UxTXREG for

the Break character is ignored. The write simply serves the purpose of initiating the proper

sequence – all ‘0’s will be transmitted.

The UTXBRK bit is automatically reset by hardware after the corresponding Stop bit is sent. This

allows the user application to preload the transmit FIFO with the next transmit byte, following the

Break character (typically, the Sync character in the LIN/J2602 specification).

The TRMT bit indicates when the Transmit Shift Register is empty or full, just as it does during

the normal transmission. See Figure 5-5 for the timing of the Break character sequence.

Figure 5-5: Send Break Character Sequence

5.4.1 BREAK AND SYNC TRANSMIT SEQUENCE

The following sequence sends a message frame header made up of a Break, followed by an

auto-baud Sync byte. This sequence is typical of a LIN/J2602 bus master.

1. Configure the UART for the desired mode.

2. Set the UTXEN and UTXBRK bits to transmit the Break character.

3. Load the UxTXREG with a dummy character to initiate transmission (value is ignored).

4. Write 0x55 to UxTXREG – loads the Sync character into the transmit FIFO.

After the Break has been sent, the UTXBRK bit is reset by hardware. The Sync character is now

transmitted.

Note: The user application should wait for the transmitter to be Idle (TRMT = 1) before set-

ting the UTXBRK bit. The UTXBRK bit overrides any other transmitter activity. If the

user application clears the TXBRK bit prior to sequence completion, unexpected

module behavior can result. Sending a Break character does not generate a

transmit interrupt.

Write to UxTXREG

Start bit bit 0 bit 1 bit 11 Stop bit

Break

UxTX

TRMT bit

UTXBRK Sampled Here

Auto-Cleared

UTXBRK bit

UxTXIF

BCLKx/16

(Shift Clock)

Dummy Write

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6.0 DATA BIT DETECTION

6.1 16X Clock Mode (BRGH = 0)

In 16x Clock mode, each bit of the received data is 16 clock pulses wide. To detect the value of

an incoming data bit, the bit is sampled at the 7th, 8th and 9th rising edges of the clock. These

rising edges are called Majority Detection edges. This mode is more robust than 4x Clock mode.

Figure 6-1: 16x Clock Mode with Majority Detection

6.2 4X Clock Mode (BRGH = 1)

In 4x Clock mode, each bit of the received data is four clock pulses wide. The 4x Clock mode

does not provide enough edges to support the Majority Detection method. Therefore, the

received data is sampled at the one-half bit width.

Figure 6-2: 4x Clock Mode without Majority Detection

Note: In 16x Clock mode, each bit is sampled at 7th, 8th and 9th rising edges of the clock.

Idle Start bit bit 0

MD2

MD3

MD1

Start Bit Detected

16x Clock

Bit Clock

Internal Bit Counter

(Received Data)

Start bit bit 0 bit 1

Sample Point

4x Clock

Bit Clock

Internal Bit Counter

Note: In 4x Clock mode, the sampling occurs only at the one-half bit width.

 2009-2013 Microchip Technology Inc. DS70000582E-page 21

UART

7.0 UART RECEIVER

The receiver block diagram of the UART module is illustrated in Figure 7-1. The important part

of the receiver is the UARTx Receive (Serial) Shift Register (UxRSR). The data is received on

the UxRX pin and is sent to the data recovery block. After sampling the UxRX pin for the Stop bit,

the received data in the UxRSR register is transferred to the receive FIFO (if it is empty). The

data recovery block operates at 16 times the baud rate, whereas the main receive serial shifter

operates at the baud rate.

The data on the UxRX pin is sampled multiple times by a Majority Detect circuit to determine if a

high or a low level is present at the UxRX pin.

7.1 Receive Buffer (UxRXREG)

The UART receiver has a 4 deep, 9-bit wide FIFO receive data buffer. The UxRXREG is a

memory mapped register that provides access to the output of the FIFO. It is possible for four

words of data to be received and transferred to the FIFO, and a fifth word to begin shifting to the

UxRSR register before a buffer overrun occurs.

7.2 Receiver Error Handling

If the FIFO is full (four characters) and a fifth character is fully received into the UxRSR register,

the OERR bit (UxSTA<1>) will be set. The word in the UxRSR register will be kept, but further

transfers to the receive FIFO and UART interrupts are inhibited as long as the OERR bit is set.

The user application must clear the OERR bit in software to allow further data to be received.

If it is desired to keep the data received prior to the overrun, the user application should first read

all five characters, then clear the OERR bit. If the five characters can be discarded, the user

application can simply clear the OERR bit. This effectively resets the receive FIFO and all prior

received data is lost.

The Framing Error bit, FERR (UxSTA<2>), is set if a Stop bit is detected at a logic low level.

The Parity Error bit, PERR (UxSTA<3>), is set if a parity error has been detected in the data word

at the top of the buffer (i.e., the current word). For example, a parity error would occur if the parity

is set to be even, but the total number of ‘1’s in the data has been detected to be odd. The PERR

bit is irrelevant in 9-bit mode. The FERR and PERR bits are buffered along with the

corresponding word and should be read before reading the data word.

An interrupt is generated if any of these (OERR, FERR and PERR) errors occur. The user

application needs to enable the corresponding UARTx Interrupt Enable Control bit (UxERIE) in

the IECx register to go to the corresponding interrupt vector location.

Note: The UxRSR register is not mapped in the data memory, so it is not available to the

user application.

Note: The data in the receive FIFO should be read prior to clearing the OERR bit. The

FIFO is reset when OERR is cleared, which causes all data in the buffer to be lost.

Note: After a Reset, the three possible UART interrupts have the same Interrupt Priority

Level (IPL). Natural order allows the (RX/TX) data interrupts to be serviced before

the UART error interrupt.

To allow the UART error interrupt to be serviced before the (RX/TX) data interrupts,

its Interrupt Priority Level (UxEIP) is raised or the data Interrupt Priority Levels are

lowered (UxRXIP and UxTXIP).

Example for UART2 to raise the UART2 error interrupt level:

• IPC7bits.U2RXIP = 4; //UART2 RX interrupt priority, mid-range

• IPC7bits.U2TXIP = 4; //UART2 TX interrupt priority, mid-range

• IPC16bits.U2EIP = 5; //UART2 error priority set higher

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7.3 Receive Interrupt

The UARTx Receive Interrupt Flag (UxRXIF) bit is located in the corresponding Interrupt Flag

Status x register (IFSx). The URXISEL<1:0> control bits (UxSTA<7:6>) determine when the

UART receiver generates an interrupt.

• If URXISEL<1:0> = 00 or 01, an interrupt is generated each time a data word is transferred

from the UARTx Receive Shift Register (UxRSR) to the receive buffer. There may be one or

more characters in the receive buffer.

• If URXISEL<1:0> = 10, an interrupt is generated when a word is transferred from the

UxRSR register to the receive buffer, and as a result, the receive buffer contains three or

four characters.

• If URXISEL<1:0> = 11, an interrupt is generated when a word is transferred from the

UxRSR register to the receive buffer, and as a result, the receive buffer contains four

characters (i.e., becomes full).

Switching between the three Interrupt modes during operation is possible.

While the URXDA and UxRXIF flag bits indicate the status of the UxRXREG register, the RIDLE

bit (UxSTA<4>) shows the status of the UxRSR register. The RIDLE status bit is a read-only bit

and is set when the receiver is Idle (i.e., the UxRSR register is empty). No interrupt logic is tied

to this bit, so the user application needs to poll this bit in order to determine if the UxRSR register

is Idle.

The URXDA bit (UxSTA<0>) is a read-only bit, which indicates whether the receive buffer has

data or is empty. This bit is set as long as there is at least one character to be read from the

receive buffer.

Figure 7-1 illustrates a block diagram of the UART receiver.

 2009-2013 Microchip Technology Inc. DS70000582E-page 23

UART

Figure 7-1: UARTx Receiver Block Diagram

URX8 UxRXREG Low Byte

Load UxRSR

UxMODE

Receive Buffer Control

– Generate Flags

– Generate Interrupt

UxRXIF

UxRX

• Start bit Detect

Receive Shift Register

Control

Signals

16x Baud Clock

from Baud Rate

Generator

UxSTA

– Shift Data Characters

to Buffer

(UxRSR)

PERR

FERR

• Parity Check

• Stop bit Detect

• Shift Clock Generation

• Wake Logic

Internal Data Bus

LPBACK

From UxTX

15 9 8 7 0

Word Word or

Byte Read

BCLKx/UxRTS

UxCTS

Selection

UEN

BCLKx

UEN1

UEN0

 16 Divider

UxRTS

UxCTS

Note: The ‘x’ denotes the UART number.

Read-Only

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7.4 Setup for UART Reception

The following steps are used to set up a UART reception:

1. Initialize the UxBRG register for the appropriate baud rate (see Section 3.0 “UART Baud

Rate Generator”).

2. Set the number of data bits, number of Stop bits and parity selection by writing to the

PDSEL<1:0> (UxMODE<2:1>) and STSEL (UxMODE<0>) bits.

3. If interrupts are desired, set the UxRXIE bit in the corresponding Interrupt Enable

Control x register (IECx).

Specify the interrupt priority for the interrupt using the UxRXIP<2:0> control bits in the cor-

responding Interrupt Priority Control x register (IPCx). Also, select the Receive Interrupt

mode by writing to the URXISEL<1:0> bits (UxSTA<7:6>).

4. Enable the UART module by setting the UARTEN bit (UxMODE<15>).

5. Receive interrupts will depend on the URXISEL<1:0> control bit settings.

If receive interrupts are not enabled, the user application can poll the URXDA bit. The

UxRXIF bit should be cleared in the software routine that services the UART receive

interrupt.

6. Read data from the receive buffer.

If 9-bit transmission is selected, read a word; otherwise, read a byte. The URXDA status

bit (UxSTA<0>) is set whenever the data is available in the buffer.

Example 7-1 provides the sample code that sets up the UART for reception.

Figure 7-2: UARTx Reception

(1,2)

Figure 7-3: UARTx Reception with Receive Overrun

Start

bit bit 1bit 0 bit 7 bit 0Stop

bit

Start

bit bit 7 Stop

bit

UxRX

RIDLE bit

Character 1

to UxRXREG

Character 2

to UxRXREG

UxRXIF

(URXISEL<1:0> =

)

Note 1: This timing diagram shows two characters received on the UxRX input.

2: If the interrupt flag is used by the application software as a basis for disabling the UART transmission, the software should

wait for 1-bit time before disabling the transmission.

Start

bit bit 7/8bit 1bit 0 bit 7/8 bit 0Stop

bit

Start

bit

Start

bitbit 7/8 Stop

bit

UxRX

OERR bit

RIDLE bit

Characters 1, 2, 3 and 4

Stored in Receive FIFO

Character 5

Held in UxRSR

Stop

bit

Character 1 Characters 2, 3, 4 and 5 Character 6

OERR Cleared by User in Software

Note: This diagram shows 6 characters received without the user reading the input buffer. The 5th character received is held in the

Receive Shift register. An overrun error occurs at the start of the 6th character.

 2009-2013 Microchip Technology Inc. DS70000582E-page 25

UART

Example 7-1: UART1 Receive Only with Polling (Interrupts Disabled)

#define FP 40000000

#define BAUDRATE 9600

#define BRGVAL ((FP/BAUD RATE)/16) - 1

int main(void)

{

// Configure oscillator as needed

U1MODEbits.STSEL = 0; // 1-stop bit

U1MODEbits.PDSEL = 0; // No Parity, 8-data bits

U1MODEbits.ABAUD = 0; // Auto-Baud disabled

U1MODEbits.BRGH = 0; // Standard-Speed mode

U1BRG = BRGVAL; // Baud Rate setting for 9600

U1STAbits.URXISEL = 0; // Interrupt after one RX character is received;

U1MODEbits.UARTEN = 1; // Enable UART

while(1)

{

char ReceivedChar;

/* Check for receive errors */

if(U1STAbits.FERR == 1)

{

continue;

}

/* Must clear the overrun error to keep UART receiving */

if(U1STAbits.OERR == 1)

{

U1STAbits.OERR = 0;

continue;

}

/* Get the data */

if(U1STAbits.URXDA == 1)

{

ReceivedChar = U1RXREG;

}

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8.0 USING THE UART FOR 9-BIT COMMUNICATION

The UART receiver can be used in 9-Bit Data mode for multiprocessor communication. With the

ADDEN bit set in 9-Bit Data mode, the receiver can ignore the data when the 9th bit of the data

is ‘0’. This feature can be used in a multiprocessor environment.

8.1 Multiprocessor Communications

A typical multiprocessor communication protocol will differentiate between the data bytes and the

address/control bytes. A common scheme is to use a 9th data bit to identify whether a data byte

is address or data information. If the 9th bit is set, the data is processed as address or control

information. If the 9th bit is cleared, the received data word is processed as data associated with

the previous address/control byte.

The protocol operates as follows:

• The master device transmits a data word with the 9th bit set. The data word contains the

address of a slave device.

• All slave devices in the communication chain receive the address word and check the slave

address value.

• The slave device that was addressed will receive and process subsequent data bytes sent

by the master device. All other slave devices will discard subsequent data bytes until a new

address word (9th bit set) is received.

8.2 ADDEN Control Bit

The UART receiver has an Address Detect mode, which allows it to ignore data words with the

9th bit cleared. This reduces the interrupt overhead because the data words with the 9th bit

cleared are not buffered. This feature is enabled by setting the ADDEN bit (UxSTA<5>).

The UART must be configured for 9-bit Data mode to use the Address Detect mode. The ADDEN

bit has no effect when the receiver is configured in 8-bit Data mode.

8.3 Setup for 9-Bit Transmit

The setup procedure for 9-bit transmission is identical to the procedure for 8-Bit Transmit modes,

except that the PDSEL<1:0> bits (UxMODE<2:1>) should be set to ‘11’ (see Section 5.3 “Setup

for UART Transmit”).

Word writes should be performed to the UxTXREG register (starts transmission).

 2009-2013 Microchip Technology Inc. DS70000582E-page 27

UART

8.4 Setup for 9-Bit Reception Using Address Detect Mode

The setup procedure for 9-bit reception is similar to the procedure for 8-Bit Receive modes,

except that the PDSEL<1:0> bits (UxMODE<2:1>) should be set to ‘11’ (see Section 7.4 “Setup

for UART Reception”).

The Receive Interrupt mode should be configured by writing to the URXISEL<1:0>

(UxSTA<7:6>) bits.

The procedure for using the Address Detect mode is as follows:

1. Set the ADDEN bit (UxSTA<5>) to enable address detect. Ensure that the URXISEL<1:0>

control bits are configured to generate an interrupt after each received word.

2. Check each 8-bit address by reading the UxRXREG register to determine if the device is

being addressed.

3. If this device has not been addressed, discard the received word.

4. If this device has been addressed, clear the ADDEN bit to allow subsequent data bytes to

be read into the receive buffer and interrupt the CPU.

If a long data packet is expected, the Receive Interrupt mode can be changed to buffer

more than one data byte between the interrupts.

5. After receiving the last data byte, set the ADDEN bit so that only address bytes are

received.

Also, ensure that the URXISELx control bits are configured to generate an interrupt after

each received word.

Figure 8-1: UARTx Reception with Address Detect (ADDEN = 1)

Note: If the Address Detect mode is enabled (ADDEN = 1), the URXISEL<1:0> control bits

should be configured so that an interrupt will be generated after every received

word. Each received data word must be checked in software for an address match

immediately after reception.

Start

bit bit 1bit 0 bit 8 bit 0Stop

bit

Start

bit bit 8 Stop

bit

UxRX (pin)

Read Rcv

Buffer Register

UxRXREG

UxRXIF

(Interrupt Flag)

Word 1

UxRXREG

bit 8 = 0, Data Byte bit 8 = 1, Address Byte

Transfer

to Receive FIFO

Note: This timing diagram shows a data byte followed by an address byte. The data byte is not read into the UxRXREG (receive buffer)

because ADDEN = 1 and bit 8 = 0.

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8.5 Address Match Detect

The UART has a built-in feature that can perform address match detection to off-load this task from

the processors. The ADM_ADD<7:0> (UxADMD<7:0>) address and ADM_MASK<7:0>

(UxADMD<15:8>) address mask bits are used to hold the desired address and mask bits, respec-

tively. If ADDEN = 1 and the 9th bit received is a ‘1’, the data in the Receive Shift register is

compared to the ADM_ADDx bits and masked with the ADM_MASKx bits. If a match is found, the

data is transferred from the Receive Shift register to the UxRXBUF according to Table 8-1.

If an address match is found, software must clear ADDEN = 0 to receive the remainder of the

message; interrupts on the body of the message will occur as specified by URXISEL<1:0>

(UxSTA<7:6>). After the body of the message is received, software must set ADDEN = 1 to

enable Address Detect mode once again.

8.5.1 USING ADDRESS MATCH DETECT

The setup procedure for 9-bit reception is similar to the procedure for 8-Bit Receive modes,

except that the PDSEL<1:0> bits (UxMODE<2:1>) should be set to ‘11’ (see Section 7.4 “Setup

for UART Reception”).

1. Write the desired match address to ADM_ADDR<7:0>.

2. Write the desired address mask to ADM_MASK<7:0>.

3. Set PDSEL<1:0> = 11 to choose 9-bit mode.

4. Set ADDEN = 1 to enable automatic address detection.

5. When an interrupt is received, the matching address will be stored in the UxRXBUF. If a

mask is being used for decision logic, user software can read it from UxRXBUF. If the

address is not needed, it should be cleared from the buffer with a dummy read.

6. Clear ADDEN to allow the reception of the following data. Interrupts on the body of the

message will occur as specified by URXISEL<1:0>.

7. When reception of the body of message is completed (as determined in the application

software), set the ADDEN bit to ‘1’ to detect the next message address.

Note: Not all devices support address match detect. Refer to the specific device data

sheet for availability.

Table 8-1: Address Match Detection

Condition Action

(UxRSR<7:0> and ADM_MASK<7:0>) = (ADM_ADDR<7:0>

and ADM_MASK<7:0>)

(1)

UxBUF = UxRSR<7:0>

(UxRSR<7:0> and ADM_MASK<7:0>) ≠ (ADM_ADDR<7:0>

and ADM_MASK<7:0>)

(1)

None, UxRSR will be

overwritten with next

incoming byte

Note 1: ADM_MASKx bits set to ‘0’ are regarded as ‘don’t care’ for that address bit position.

Note: The URXISEL<1:0> control bits do not have any impact on the interrupt generation

in this mode. If the 9th bit is a ‘1’, an interrupt is generated, regardless of the state

of the URXISEL<1:0> bits.

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UART

9.0 OTHER FEATURES OF THE UART

9.1 UART in Loopback Mode

Setting the LPBACK bit (UxMODE<6>) enables the Loopback mode, in which the UxTX output

is internally connected to the UxRX input. When configured for the Loopback mode, the UxRX

pin is disconnected from the internal UART receive logic. However, the UxTX pin still functions

normally.

To select Loopback mode, follow these steps:

1. Configure the UART module for the desired mode of operation.

2. Enable transmission as defined in Section 5.0 “UART Transmitter”.

3. Set the LPBACK bit = 1 to enable Loopback mode.

The Loopback mode is dependent on the UEN<1:0> bits, as shown in Tab l e 9-1.

Table 9-1: Loopback Mode Pin Function

9.2 Auto-Baud Support

To allow the system to determine baud rates of the received characters, the ABAUD bit

(UxMODE<5>) is enabled. The UART begins an automatic baud rate measurement sequence

whenever a Start bit is received while the Auto-Baud Rate Detect is enabled (ABAUD = 1). The

calculation is self-averaging. Once the ABAUD bit is set, the BRG counter value will be cleared

and will look for a Start bit, which in this case, is defined as a high-to-low transition, followed by

a low-to-high transition.

Following the Start bit, the auto-baud expects to receive an ASCII “U” (“55h”) in order to

calculate the proper bit rate. The measurement is taken over both the low and the high bit time

in order to minimize any effects caused by asymmetry of the incoming signal. On the 5th UxRX

pin rising edge, an accumulated BRG counter value, totaling the proper BRG period, is

transferred to the UxBRG register. The ABAUD bit is automatically cleared. If the user

application clears the ABAUD bit prior to sequence completion, unexpected module behavior

can result. See Figure 9-1 for the Auto-Baud Rate Detection sequence.

UEN<1:0>

Pin Function, LPBACK = 1

(1)

00 UxRX input connected to UxTX; UxTX pin functions; UxRX pin ignored; UxCTS/

UxRTS

unused

01 UxRX input connected to UxTX; UxTX pin functions; UxRX pin ignored;

UxRTS

pin functions; UxCTS unused

10 UxRX input connected to UxTX; UxTX pin functions; UxRX pin ignored;

UxRTS

pin functions; UxCTS input connected to UxRTS; UxCTS pin ignored

11 UxRX input connected to UxTX; UxTX pin functions; UxRX pin ignored;

BCLKx pin functions; UxCTS

/UxRTS unused

Note 1: The LPBACK bit should be set to ‘1’ only after enabling the other bits associated

with the UART module.

Note: Depending on the specific device used, the ABAUD feature of a respective UART

may automatically use the corresponding Input Capture x (ICx) peripheral for

UARTx auto-baud measurements. For devices that use the corresponding ICx

peripheral, the user application should not use the respective ICx peripheral for

other purposes. See the specific device data sheet regarding this dependency.

dsPIC33/PIC24 Family Reference Manual

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Figure 9-1: Automatic Baud Rate Calculation

While the auto-baud sequence is in progress, the UART state machine is held in an Idle state.

The UxRXIF interrupt is set on the 5th UxRX rising edge, independent of the URXISEL<1:0> bits

setting. The receiver FIFO is not updated.

BRG Counter

UxRX

ABAUD bit

bit 0 bit 1

BRG Clock

Start

Auto-Cleared

Set by User Software

XXXXh 0000h

Edge 1

bit 2 bit 3

Edge 2

bit 4 bit 5

Edge 3

bit 6 bit 7

Edge 4

Stop bit

Edge 5

001Ch

BRG Register

XXXXh 001Ch

UxRXIF

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UART

10.0 UART OPERATION WITH DMA

On some dsPIC33 and PIC24 devices, the Direct Memory Access (DMA) module can be used

to transfer data between the CPU and UART without CPU assistance. Refer to the specific

device data sheet to see if DMA is present on your particular device. For more information on the

DMA module, refer to the Direct Memory Access (DMA) FRM that pertains to the specific device

being used.

10.1 UART Receive with DMA

If the DMA channel is associated with the UART receiver, the UART should issue a DMA request

every time there is a character ready to be moved from the UART module to RAM. The DMA

transfers data from the UxRXREG register into RAM and issues a CPU interrupt after a pre-

defined number of transfers. As the DMA channels are unidirectional, the UART receive

operation would require one DMA channel.

The UART module must be configured to generate interrupts for every character received. For

the UART receiver to generate an RX interrupt for each character received, the UART Receive

Interrupt Mode Selection bits (URXISEL<1:0>) must be set to ‘00’ or ‘01’ in the Status and Con-

trol register (UxSTA). When the UART and DMA channel are properly configured, the UART

receiver issues a DMA request as soon as data is received. No special steps need to be taken

by the user application to initiate a DMA transfer.

While configuring for UART reception, the word size of the DMA channel should be set to 16-bit.

This configures the DMA channel to read 16 bits from the UART module when data is available to

be read. The lower byte of the data represents the actual data byte received by the UART module.

The upper byte contains the UART status when the byte was received. Note that the reading of the

UxSTA register, when the UART reception is DMA enabled, will not return the status of the FERR

and PERR bits. This status is available in the upper byte of the 16-bit word that the DMA channel

transfers from the UART module to DMA RAM. Figure 10-1 illustrates the organization of the 16-bit

word transferred by DMA from the UART module to the DMA RAM.

Figure 10-1: Format of 16-Bit UART Receive Data Word Transferred by DMA to RAM

The UARTx Error Interrupt Flag bit (UxEIF) gets set if the last UART reception caused a framing

or a parity error. Setting the UxEIE bit causes the CPU to enter the UART error Interrupt Service

Routine (ISR). The user application can then inspect the upper byte of the last transferred word

to check which error condition has caused the interrupt.

—

12 10 9 bit 0711bit 15 8

Received UART Byte—FERR—PERR

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10.2 UART Transmit with DMA

If the DMA channel is associated with the UART transmitter, the UART issues a DMA request

after each successful transmission. After each DMA request, the DMA transfers new data into

the UxTXREG register and issues a CPU interrupt after a predefined number of transfers. As the

DMA channels are unidirectional, one DMA channel is required for transmit.

In addition, the UART must be configured to generate interrupts for every character transmitted.

For the UART transmitter to generate a TX interrupt for each character transmitted, the UART

Transmission Interrupt Mode Selection bits (UTXISEL0 and UTXISEL1) must be set to ‘0’ in the

UxSTA register.

The UART transmitter issues a DMA request as soon as the UART and transmitter are enabled.

This means that the DMA channel and buffers must be initialized and enabled before the UART

and transmitter are enabled.

Note: For PIC24H, PIC24EP and dsPIC

devices only, alternatively, the UART transmitter

can be enabled before the DMA channel is enabled. In this case, the UART trans-

mitter DMA request will be lost and the user application must issue a DMA request

to start DMA transfers by setting the FORCE bit in the DMAxREQ register.

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UART

11.0 UART OPERATION DURING CPU SLEEP AND IDLE MODES

11.1 UART Operation in Sleep Mode

When the device enters Sleep mode, all clock sources supplied to the UART module are shut

down and stay at logic ‘0’. If the device enters Sleep mode in the middle of a UART transmission

or reception operation, the operation is aborted and the UARTx pins (BCLKx, UxRTS and UxTX)

are driven to the default state.

A Start bit, when detected on the UARTx Receive pin (UxRX), can wake up the device from Sleep

mode if the WAKE bit (UxMODE<7>) is set just before the device enters Sleep mode. In this

mode, if the UARTx Receive Interrupt (UxRXIE) is enabled, a falling edge on the UART receive

pin generates a UARTx Receive Interrupt Flag (UxRXIF).

The receive interrupt wakes up the device from Sleep and the following events occur:

• If the assigned priority for the interrupt is less than or equal to the current CPU priority, the

device wakes up and continues code execution from the instruction following the PWRSAV

instruction that initiated Sleep mode.

• If the assigned priority level for the interrupt source is greater than the current CPU priority,

the device wakes up and the CPU execution process begins. Code execution continues

from the first instruction of the captured ISR.

• The UART does not recognize the first character received after a wake from Sleep due to

the delay in restoration of the clocks after the oscillator restart.

The WAKE bit is automatically cleared when a low-to-high transition is observed on the UxRX

line following the wake-up event.

11.2 UART Operation in Idle Mode

• When the device enters Idle mode, the system clock sources remain functional, but the

CPU stops code execution. The UART Stop in Idle bit (USIDL) in the UARTx Mode register

(UxMODE<13>) determines whether the module stops in Idle mode or continues to operate

in Idle mode.

•If USIDL = 0, the module continues to operate in Idle mode and provides full functionality.

•If USIDL = 1, the module stops in Idle mode. The module performs the same functions

when stopped in Idle mode as in Sleep mode (refer to Section 11.1 “UART Operation in

Sleep Mode”).

11.3 Auto-Wake-up on Sync Break Character

The auto-wake-up feature is enabled with the WAKE bit (UxMODE<7>). Once WAKE is active,

the typical receive sequence on UxRX is disabled. Following the wake-up event, the module

generates the UxRXIF interrupt.

The LPBACK bit (UxMODE<6>) must equal ‘0’ for wake-up to operate.

A wake-up event consists of a high-to-low transition on the UxRX line. This coincides with the

start of a Sync Break or a Wake-up Signal character for the LIN/J2602 protocol. When WAKE is

active, the UxRX line is monitored independently from the CPU mode. The UxRXIF interrupt will

be generated synchronously to the Q clocks in normal user mode, and asynchronously, if the

module is disabled due to Sleep or Idle mode. To assure that no actual data is lost, the WAKE bit

should be set just prior to entering the Sleep mode and while the UART module is in Idle.

The WAKE bit is automatically cleared once a low-to-high transition is observed on the UxRX line

following the wake-up event. At this point, the UART module is in Idle mode and is returned to

normal operation. This signals to the user that the Sync Break event is over. If the user clears the

WAKE bit prior to sequence completion, unexpected module behavior can result.

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The wake-up event causes a receive interrupt by setting the UxRXIF bit. The UARTx Receive

Interrupt Select mode bits (URXISEL<1:0>) are ignored for this function. If the UxRXIF interrupt

is enabled, then this will wake up the device.

Figure 11-1: Auto-Wake-up Bit (WAKE) Timings During Normal Operation

Figure 11-2: Auto-Wake-up Bit (WAKE) Timings During Sleep

Note 1: The Sync Break (or Wake-up Signal) character must be of sufficient length to allow

enough time for the selected oscillator to start and provide proper initialization to

the UART. To ensure that the UART wakes up in time, the user application should

read the value of the WAKE bit (UxMODE<7>). If it is clear, it is possible that the

UART was not ready in time to receive the next character and the module might

need to be resynchronized to the bus.

2: In Sleep mode, a Start bit, when detected, causes the device to wake up only if the

WAKE bit (UxMODE<7>) is set just before the device enters Sleep mode.

3: In Sleep and Idle modes, as the falling edge on the UART receive pin generates a

UART receive interrupt, a dummy byte is copied if the UART receive buffer is read

in the first UART receive interrupt.

OSC1

WAKE bit

(1)

UxRX

UxRXIF

Note 1: UARTx state machine is held in Idle while WAKE bit is active.

Bit Set by User

Auto-Cleared

OSC1

WAKE bit

(2)

UxRX

UxRXIF

Sleep

Note 1: If the wake-up event requires a long oscillator warm-up time, the auto-clear of the WAKE bit can occur while the system

clocks are still active. This sequence should not depend on the presence of F

2: The UARTx state machine is held in Idle while the WAKE bit is active.

(Note 1)

Bit Set by

Auto-Cleared

User Software

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UART

12.0 OPERATION OF UxCTS AND UxRTS CONTROL PINS

The UxCTS (Clear-to-Send) and UxRTS (Request-to-Send) pins are the two hardware controlled

pins associated with the UART module. These two pins allow the UART to operate in Flow Con-

trol and Simplex modes, which are explained in detail in Section 12.2 “UxRTS Function in Flow

Control Mode” and Section 12.3 “UxRTS Function in Simplex Mode”, respectively. They are

implemented to control transmission and reception between the UART and Data Terminal

Equipment (DTE).

12.1 UxCTS Function

During UART operation, the UxCTS pin acts as an input pin, which can control the transmission.

This pin is controlled by another device (typically a PC). The UxCTS

pin is configured using the

UEN<1:0> bits (UxMODE<9:8>).

• When UEN<1:0> = 10, UxCTS is configured as an input.

• If UxCTS

= 1, the transmitter will go as far as loading the data in the Transmit Shift Register,

but will not initiate a transmission. This will allow the DTE to control and receive data from the

controller per its requirements.

The UxCTS

pin is sampled while the transmit data changes (i.e., at the beginning of the 16 baud

clocks). The transmission begins only when the UxCTS

is sampled low. The UxCTS is sampled

internally with a T

P, which means that there should be a minimum pulse width of 1 TP on UxCTS.

However, this cannot be a specification as the T

P can vary depending on the clock used.

The user application can also read the status of the UxCTS

by reading the associated port pin.

12.2 UxRTS Function in Flow Control Mode

During Flow Control mode, the UxRTS pin of one DTE is connected to the UxCTS pin of the

dsPIC33 or PIC24 device, and the UxCTS

pin of the DTE is connected to the UxRTS pin of the

device, as illustrated in Figure 12-1. The UxRTS

signal indicates that the device is ready to

receive the data. The UxRTS

pin is driven as an output whenever UEN<1:0> = 01 or 10. The

UxRTS

pin is asserted (driven low) whenever the receiver is ready to receive data. When the

RTSMD bit = 0 (when the device is in Flow Control mode), the UxRTS

pin is driven low whenever

the receive buffer is not full or the OERR bit is not set. When the RTSMD bit = 0, the UxRTS

is driven high whenever the device is not ready to receive (i.e., when the receiver buffer is either

full or in the process of shifting).

Since the UxRTS

pin of the DTE is connected to the UxCTS pin of the dsPIC33 and PIC24

devices, the UxRTS

pin drives the UxCTS pin low whenever it is ready to receive the data. Trans-

mission of the data begins when the UxCTS

pin goes low, as explained in Section 12.1 “UxCTS

Function”.

12.3 UxRTS Function in Simplex Mode

During Simplex mode, the UxRTS pin of the DCE is connected to the UxRTS pin of the dsPIC33

or PIC24 device, and the UxCTS

pin of the DCE is connected to the UxCTS pin of the device, as

illustrated in Figure 12-2. In Simplex mode, the UxRTS

signal indicates that the DTE is ready to

transmit. The DCE replies to the UxRTS

signal with the valid UxCTS whenever the DCE is ready

to receive the transmission. When the DTE receives a valid UxCTS

signal, it will begin

transmission.

As illustrated in Figure 12-3, Simplex mode is also used in IEEE-485 systems to enable trans-

mitters. When UxRTS

indicates that the DTE is ready to transmit, the UxRTS signal enables the

driver.

Note: The UxCTS and UxRTS pins are not available on all devices. Refer to the “Universal

Asynchronous Receiver Transmitter (UART)” chapter of the specific device data

sheet for availability.

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 36  2009-2013 Microchip Technology Inc.

The UxRTS pin is configured as an output and is driven whenever UEN<1:0> = 01 or 10. When

RTSMD = 1, the UxRTS

is asserted (driven low) whenever data is available to transmit

(TRMT = 0). When RTSMD = 1, UxRTS

is deasserted (driven high) when the transmitter is

empty (TRMT = 1).

Figure 12-1: UxRTS

/UxCTS Flow Control for DTE-DTE (RTSMD = 0, Flow Control Mode)

Figure 12-2: UxRTS

/UxCTS Handshake for DTE-DCE (RTSMD = 1, Simplex Mode)

Figure 12-3: UxRTS

/UxCTS Bus Enable for IEEE-485 Systems (RTSMD = 1)

UxRTS

UxCTS UxCTS

DTE

(Typically a PC)

DTE

(Typically another System or dsPIC33E/PIC24E)

I am ready to receive

I’ll transmit if OK

I am ready to receive

I will transmit if OK

UxRTS

UxCTS

DCE

(Typically a Modem)

May I send something?

UxRTS

active and receiver ready

I will transmit if OK

OK, go ahead and send

DTE

(Typically a dsPIC33/PIC24)

UxRTS

UxCTS

DTE

(Typically a dsPIC33/PIC24)

May I transmit something?

I will transmit if OK

UxTX

UxRX

TTL to RS-485

Transceiver

Integrated CKT

 2009-2013 Microchip Technology Inc. DS70000582E-page 37

UART

13.0 INFRARED SUPPORT

The UART module provides two types of infrared UART support: one is the IrDA

clock output

to support the external IrDA encoder and decoder devices (legacy module support), and the

other is the full implementation of the IrDA encoder and decoder.

13.1 External IrDA Support – IrDA Clock Output

To support external IrDA encoder and decoder devices, the BCLKx pin can be configured to gen-

erate the 16x baud clock. When UEN<1:0> = 11, the BCLKx pin outputs the 16x baud clock if

the UART module is enabled; this pin can be used to support the IrDA codec chip.

13.2 Built-in IrDA Encoder and Decoder

The UART has full implementation of the IrDA encoder and decoder. The built-in IrDA encoder

and decoder functionality is enabled using the IREN bit (UxMODE<12>). When enabled

(IREN = 1), the receive pin (UxRX) acts as an input from the infrared receiver. The transmit pin

(UxTX) acts as an output to the infrared transmitter.

13.2.1 IrDA ENCODER FUNCTION

The encoder works by taking the serial data from the UART and replacing it. Transmit bit data of

‘1’ becomes encoded as ‘0’ for the entire 16 periods of the 16x baud clock. Transmit bit data of

‘0’ becomes encoded as ‘0’ for the first 7 periods of the 16x baud clock, as ‘1’ for the next

3 periods and as ‘0’ for the remaining 6 periods. See Figure 13-1 and Figure 13-3 for details.

13.2.2 TRANSMIT POLARITY

The transmit polarity is selected using the UTXINV bit (UxSTA<14>). When UTXINV = 0, the Idle

state of the UxTX line is ‘0’ (see Figure 13-1). When UTXINV = 1, the Idle state of the UxTX line

is ‘1’ (see Figure 13-2).

Figure 13-1: IrDA

Encode Scheme

Figure 13-2: IrDA

Encode Scheme for ‘0’ Bit Data

Note: This feature is available only in Standard Speed mode (BRGH = 0) with a baud rate

above 1200 baud.

Note: Some devices may have a 16x baud clock output (BCLKx) Idle state as a logic high.

UxTX Data

UxTX

UxTX Data

UxTX

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Figure 13-3: IrDA

Encode Scheme for ‘0’ Bit Data with Respect to 16x Baud Clock

13.2.3 IrDA DECODER FUNCTION

The decoder works by taking the serial data from the UxRX pin and replacing it with the decoded

data stream. The stream is decoded based on falling edge detection of the UxRX input.

Each falling edge of UxRX causes the decoded data to be driven low for 16 periods of the

16x baud clock. If, by the time the 16 periods expire, another falling edge is detected, the

decoded data remains low for another 16 periods. If no falling edge was detected, the decoded

data is driven high.

Note that the data stream into the device is shifted anywhere from 7 to 8 periods of the 16x baud

clock from the actual message source. The one clock uncertainty is due to the clock edge

resolution (see Figure 13-4 for details).

Figure 13-4: IrDA

Decoding Scheme

13.2.4 IrDA RECEIVE POLARITY

The input of the IrDA signal can have an inverted polarity. The same logic is able to decode the

signal train, but in this case, the decoded data stream is shifted from 10 to 11 periods of the

16x baud clock from the original message source. Again, the one clock uncertainty is due to the

clock edge resolution (see Figure 13-5 for details).

Figure 13-5: Inverted Polarity Decoding Results

Start ofStart of

‘0’ Transmit bit

16x Baud Clock

UxTX Data

UxTX

8th Period 11th Period

16 Periods 16 Periods 16 Periods 16 Periods 16 Periods

Start BRG

IRDEL

Before IrDA

Encoder

UxRX

Decoded Data

(Transmitting Device)

16 Periods 16 Periods 16 Periods 16 Periods 16 Periods

Start BRG TIRDELI

Before IrDA

Encoder

UxRX

Decoded Data

(Transmitting Device)

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UART

13.2.5 CLOCK JITTER

Due to jitter or slight frequency differences between devices, it is possible for the next falling bit

edge to be missed for one of the 16x periods. In that case, a one clock wide pulse appears on

the decoded data stream. Since the UART performs a Majority Detect around the bit center, this

does not cause erroneous data (see Figure 13-6 for details).

Figure 13-6: Clock Jitter Causing a Pulse Between Consecutive Zeros

16 Periods 16 Periods

Extra Pulse will be Ignored

UxRX (rx_in)

Decoded Data

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14.0 LIN/J2602 SUPPORT

The LIN/J2602 protocol transmits data in the form of small blocks, known as frames. Each frame

consists of a Break character with a delimiter, a Sync byte, a protected identifier and the data to

be transmitted (see Figure 14-1).

• Break Sequence: The Break sequence indicates the beginning of a new frame. A Break

sequence generated by the master node consists of a Start bit, followed by twelve bits of ‘0’

and a break delimiter.

• Sync Byte: The Sync is a byte field loaded with the data value of 0x55. When the Auto-

Baud feature is enabled, the UART module uses the Sync byte to compute the baud rate of

the incoming data.

• Protected Identifier: The Protected Identifier contains the identifier and the identifier parity.

Figure 14-1: Frame Structure

14.1 Data Reception Using LIN/J2602 Protocol

When the LIN/J2602 protocol is used, the UART module receives data in the form of frames and

the incoming data is loaded into the receive buffer. For effective data reception, the BRG counter

should be loaded with the baud rate of incoming data.

The bit rate of the incoming data can be detected if the following occurs:

• The auto-baud feature is enabled

• The WAKE bit is set before setting the ABAUD bit

The UART module uses the Sync byte to compute the baud rate of the incoming data. If the

WAKE bit is set before setting the ABAUD bit, the Auto-Baud Rate Detection occurs on the byte

following the Break character. The module receives the Start bit of the Break character, the data

and the invalid Stop bit (which sets FERR), but the receiver waits for a valid Stop bit before receiv-

ing the next Start bit. No further reception can occur until a Stop bit is received. The WAKE bit is

automatically cleared once the Stop bit is received. After the fifth rising edge of the Sync

character is detected, the baud rate of the incoming data is loaded into the BRG counter and the

ABAUD bit is automatically cleared.

If the Auto-Baud feature is enabled without setting the WAKE bit, the delimiter is assumed to be

the first bit of the Sync byte instead of the Start bit. This results in erroneous baud rate calculation.

This happens because the receiver expects a Sync byte at the start of the reception. The LIN/

J2602 protocol, however, initiates the transmission with the Break character and the Sync byte

follows. Thus, the delimiter, which can range from one to four bits, is assumed to be the first low-

to-high transition on the RX line. Therefore, the delimiter acts as a first bit of the Sync byte instead

of the Start bit (see Figure 14-2).

UxRX

bit 0

bit 1

Start

bit 2

bit 3

bit 4

bit 5

bit 6

bit 7

Stop bit

Delimiter

Break Character Sync Byte

Identifier, Data

and Checksum

Note 1: Before data reception, the user application should load the BRG counter of the

UART module with a value approximate to the bit rate of the incoming data.

2: For LIN/J2602 support, the UART error interrupt (caused when FERR is set) may

need to be serviced before the (RX/TX) data interrupts. The UARTx Error Interrupt

Priority Level (UxEIP) must be raised, or the data Interrupt Priority Levels (UxRXIP

and UxTXIP) may be lowered.

Example for UART2 to raise the U2ErrInterrupt level:

• IPC7bits.U2RXIP = 4; //UART2 RX Interrupt Priority, mid-range

• IPC7bits.U2TXIP = 4; //UART2 TX Interrupt Priority, mid-range

• IPC16bits.U2EIP = 5; //UART2 Error Interrupt Priority set higher

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UART

Figure 14-2: Data Reception Using the LIN/J2602 Protocol

BRG

UxRX

bit 0

bit 1

Start

XXXXh 0000h

Edge 1

bit 2

bit 3

Edge 2

bit 4

bit 5

Edge 3

bit 6

bit 7

Edge 4

Stop bit

Edge 5

001Ch

Identifier, Data

and Checksum

Delimiter

Sync Byte

1 6

1. The user application first sets the WAKE bit and then the ABAUD bit.

2. An RX interrupt is generated because the device wakes up on the reception of the Break character.

3. The FERR bit is set.

4. The WAKE bit is cleared.

5. The auto-baud feature detects the first rising edge of the Sync byte.

6. The fifth rising edge of the Sync byte is detected. The ABAUD bit is cleared and the BRG counter is loaded with the

baud rate of the received data.

Auto-Cleared

WAKE bit

ABAUD bit

UxRXIF

52 3 4

Auto-Cleared

Counter

Break Character

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15.0 SMART CARD SUPPORT

The UART module supports communication with ISO 7816 Smart Cards. In a typical application,

the UART module is intended to act as the master or terminal that always initiates communication

transactions. The Smart Card acts as a slave and always responds to commands and other

stimulus from the terminal. Figure 15-1 shows a Smart Card subsystem using a microcontroller

with a UART module for Smart Card data communication.

The terminal is also responsible for powering, clocking and resetting the Smart Card. The clock

can be sourced by using the REFO output pin and the Reset signal can be implemented with a

general purpose output. The system is based on a half-duplex, single wire requiring that the

UART TX and UART RX pins must be shorted externally and pulled to V

DD with a weak pull-up.

The module can be configured to support either block (T = 1) or byte (T = 0) protocol. Block mode

is set up for a predetermined message block size, whereas Byte mode transmits one byte at a

time.

Upon detection of the card insertion, the terminal pulls the Reset line low to initiate a Reset

sequence. The Smart Card responds with an Answer-To-Reset (ATR), which contains parame-

ters used for communication details. The ATR baud rate is predetermined at REFO clk/372. The

terminal will need to be configured for this baud rate at the time the Reset pulse is sent to the

Smart Card. Typical REFO clock rates are 1 MHz to 5 MHz. See ISO 7816 for additional details

on ATR.

Figure 15-1: Smart Card Subsystem

Note: Some PIC

MCU devices have optional built-in support for ISO 7816 Smart Card

communication. Refer to the specific device data sheet for information regarding

Smart Card support.

Te r mi nal

dsPIC33/PIC24

UART

Smart Card

REFO

GPO

GPI

Card Detect

(1)

VDD

GND

RST

CLK

I/O

Note 1: Use a general purpose input to detect insertion of a Smart Card.

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UART

15.1 Protocol and Frame Details

The Smart Card communication scheme is based on an Elementary Time Unit (ETU) that is also

the bit clock. The Smart Card will provide the ETU value in the ATR and the terminal is configured

accordingly. A character frame consists of 10 bits; a Start bit, 8 data bits and a parity bit. Depending

on the mode, guard and wait times are used to separate bytes and message transitions.

The ISO 7816 specification defines 2 communication logic conventions: direct and inverse.

Direct convention is defined as LSB first and a high state as logic one. Inverse mode is defined

as MSB first and a low on the line is interpreted as a logic low. The logic convention is set using

the CONV bit (UxSCCON<3>).

15.1.1 GUARD TIME

Guard time is defined as the minimum delay between two consecutive character frames. The

ISO 7816 specification defines both a Character Guard Time (CGT) and a Block Guard Time

(BGT). In both T = 0 and T = 1 modes, CGT is defined as the minimum delay between the leading

edges of the two consecutive characters in the same direction of transmission. Block Guard Time

(BGT) for T = 1 mode only is defined as the minimum delay between the leading edges of the two

consecutive characters in the opposite directions. The BGT has a standard fixed value of 22 ETU.

15.1.2 WAIT TIME

Wait time is the maximum delay allowed between two consecutive characters transmitted by the

card or an interfacing device. The Character Wait Time (CWT) is the maximum delay between

the leading edges of the two consecutive characters in the block, as shown in Figure 15-2. The

minimum delay is CGT. The Block Wait Time (BWT) is the maximum delay between the leading

edge of the last character of the block received by the card and the leading edge of the first

character of the next block transmitted by the card, as shown in Figure 15-3. BWT helps the

interfacing device in detecting the unresponsive Smart Cards. The minimum delay is BGT.

Figure 15-2: Character Guard and Wait Time

Figure 15-3: Block Guard and Wait Time

Note: The guard time count is started after the parity bit is shifted out. The value of the Guard

Time Counter register will have to be calculated to exclude the character frame time.

Note: The LAST bit (UxTXREG<15>) set by user software is used to automatically start

the guard or wait timers, depending on the state of the module.

CGT ≤ t ≤ CWT

Character of a Block Next Character of the Same Block

BGT ≤ t ≤ BWT

Last Character of a Block

First Character of the Next Block

Sent by the Interface Device

Sent by the Card

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 44  2009-2013 Microchip Technology Inc.

15.1.3 ERROR DETECTION

The transmitter is responsible for calculating the parity bit value. Parity is always even, defined

as the number of logic ones and the parity bit, always being an even count. The receiver also

calculates the parity value and compares it to the received parity bit. If a discrepancy is found,

the error is flagged by the receiver, pulling the line low for a duration defined by T0PD

(UxSCCON<2>).

The transmitter tests the I/O line at Time 11 ± 0.2 ETU after the leading edge of the Start bit of a

character was sent. If the transmitter detects an error by detecting the state low on the I/O line,

it will repeat the disputed character after a delay of at least 2 ETU, following the detection of the

error. The number of repeats is configured with the TXRPT<1:0> bits (UxSCCON<5:4>). See

Figure 15-4 for timing details in T = 0 mode.

Figure 15-4: T = 0 Character Repetition Timing

Note: Protocol characteristics, electrical characteristics of the Smart Card, Answer-To-

Reset (ATR), PPS (Protocol Parameter Selection), calculation of guard time and

wait times are out of scope of this FRM. Please refer to the licensed version of the

ISO 7816-3 document for details about Smart Card communication.

Bit Clock

0 ETU

10.0 ± 0.2 ETU

(2)

10.5 ± 0.2 ETU

(3)

11.0 ± 0.2 ETU

(4)

I/O

Start Bit

Bit 0 Bit 1

(1)

Parity

Note 1: 8-bit character.

2: At 10.0 ± 0.2 ETU, the transmitter disables the driver.

3: At 10.5 ± 0.2 ETU, the receiver sets the I/O line low if a parity error is detected.

4: At 11.0 ± 0.2 ETU, the transmitter tests the I/O line.

5: See T0PD (UxSCCON<2>) in Register 15-1.

Character 1

(5)

 2009-2013 Microchip Technology Inc. DS70000582E-page 45

UART

15.2 Smart Card Control Registers

U-0 U-0 U-0 U-0 U-0 U-0 U-0 U-0

— — — — — — — —

bit 15 bit 8

U-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

— — TXRPT1

(1)

TXRPT0

(1)

CONV T0PD

(1)

PTRCL SCEN

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-6 Unimplemented: Read as ‘0’

bit 5-4 TXRPT<1:0>: Transmit Repeat Selection bits

(1)

11 = Retransmit the error byte four times

10 = Retransmit the error byte three times

01 = Retransmit the error byte twice

00 = Retransmit the error byte once

bit 3 CONV: Logic Convention Selection bit

1 = Inverse logic convention

0 = Direct logic convention

bit 2 T0PD: Pull-Down Duration for T = 0 Error Handling bit

(1)

1 = 2 ETU

0 = 1 ETU

bit 1 PTRCL: Smart Card Protocol Selection bit

1 = T = 1

0 = T = 0

bit 0 SCEN: Smart Card Mode Enable bit

1 = Smart Card mode is enabled if UARTEN (UxMODE<15>) = 1

0 = Smart Card mode is disabled

Note 1: These bits are applicable to T = 0 only. See the PTRCL bit (UxSCCON<1>.

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 46  2009-2013 Microchip Technology Inc.

U-0 U-0 R/W-0 R/W-0 U-0 U-0 R/W-0 R/W-0

— — RXRPTIF

(1)

TXRPTIF

(1)

— —WTCIFGTCIF

bit 15 bit 8

U-0 R/W-0 R/W-0 R/W-0 U-0 U-0 R/W-0 R/W-0

— PARIE RXRPTIE TXRPTIE — —WTCIEGTCIE

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-14 Unimplemented: Read as ‘0’

bit 13 RXRPTIF: Receive Repeat Interrupt Flag bit

(1)

1 = Parity error has persisted after the same character has been received five times (four retransmits)

0 = Flag is cleared

bit 12 TXRPTIF: Transmit Repeat Interrupt Flag bit

(1)

1 = Line error has been detected after the last retransmit per TXRPT<1:0> (see Register 15-1)

0 = Flag is cleared

bit 11-10 Unimplemented: Read as ‘0’

bit 9 PTRCL: Smart Card Protocol Selection bit

1 = T = 1

0 = T = 0

bit 8 SCEN: Smart Card Mode Enable bit

1 = Smart Card mode is enabled if UARTEN (UxMODE<15>) = 1

0 = Smart Card mode disabled

bit 7 Unimplemented: Read as ‘0’

bit 6 PARIE: Parity Interrupt Enable bit

1 = An interrupt is invoked when a character is received with a parity error; see the PERR bit

(UxSTA<3>) in Register 2-2 for the interrupt flag

0 = Interrupt is disabled

bit 5 RXRPTIE: Receive Repeat Interrupt Enable bit

1 = An interrupt is invoked when a parity error has persisted after the same character has been

received five times (four retransmits)

0 = Interrupt is disabled

bit 4 TXRPTIE: Transmit Repeat Interrupt Enable bit

1 = An interrupt is invoked when line error is detected after the last retransmit, per the TXRPT<1:0>

bits, has been completed (see Register 15-1)

0 = Interrupt is disabled

bit 3-2 Unimplemented: Read as ‘0’

bit 1 WTCIE: Waiting Time Counter Interrupt Enable bit

1 = Waiting Time Counter interrupt is enabled

0 = Waiting Time Counter interrupt is disabled

bit 0 GTCIE: Guard Time Counter Interrupt Enable bit

1 = Guard Time Counter interrupt is enabled

0 = Guard Time Counter interrupt is disabled

Note 1: These bits are applicable to T = 0 only. See the PTRCL bit (UxSCCON<1>.

 2009-2013 Microchip Technology Inc. DS70000582E-page 47

UART

U-0 U-0 U-0 U-0 U-0 U-0 U-0 R/W-0

— — — — — — —GTC8

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

GTC<7:0>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-9 Unimplemented: Read as ‘0’

bit 8-0 GTC<8:0>: Guard Time Counter bits

This counter is operated on the Bit Clock whose period is always equal to one ETU.

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

WTC<15:8>

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

WTC<7:0>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 8-0 WTC<15:0>: Waiting Time Counter bits

This counter is operated on the Bit Clock whose period is always equal to one ETU.

U-0 U-0 U-0 U-0 U-0 U-0 U-0 U-0

— — — — — — — —

bit 15 bit 8

R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0

WTC<23:16>

bit 7 bit 0

Legend:

R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’

-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown

bit 15-8 Unimplemented: Read as ‘0’

bit 7-0 WTC<23:16>: Waiting Time Counter bits

This counter is operated on the Bit Clock whose period is always equal to one ETU.

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 48  2009-2013 Microchip Technology Inc.

15.3 Smart Card Register Settings

The Smart Card communication protocol features are set using the UxSCCON register and the

Smart Card communication interrupts are set using the UxSCINT register. The guard and waiting

times are set using UxGTC and UxWTCL/UxWTCH registers, respectively, in units of ETU.

15.4 Smart Card Interrupt Configuration

The UART has the ability to generate interrupts reflecting the events that occur during the data

communication with the Smart Card. These interrupts can be controlled using the enable bits in

the UxSCINT register (see Register 15-2). The Smart Card protocol-specific interrupt flag status

bits can be read from the UxSCINT register and should be cleared in software.

Smart Card interrupts should be serviced in the UART error Interrupt Service Routine (ISR).

UART error interrupts must be enabled using the UxERIE bit (IECx<x>). The priority of the UART

error interrupt has to be set using UxERIP bit (IPCx<2:0>).

Example 15-1: Smart Card Interrupt Setup for UART1

15.5 Smart Card Communication

15.5.1 PRE-Answer-To-Reset (ATR) INITIALIZATION

The module should be configured in Receive mode prior to the Reset line being pulled low to

initiate the Smart Card’s response as follows:

1. Write the UxBRG register with a value corresponding to REFO/372.

2. Configure for 8-bit data, even parity, by writing PDSEL<1:0> (UxMODE<2:1>) = 11.

3. Set the SCEN bit (UxSCCON<0>).

4. Set the URXEN bit (UxSTA<12>).

5. Set up and enable the RX interrupt as described in Section 7.3 “Receive Interrupt”.

6. Enable the UART by setting the UARTEN bit (UxMODE<15>).

7. Read data out of UxRXREG as it becomes available and save for ATR processing.

Note: Smart Card bit rate (ETU) is configured by writing the appropriate value to the

UxBRG register.

// Smart card interrupt setup for UART1

U1SCINTbits.GTCIF = 0; // Clear GTC interrupt flag

U1SCINTbits.GTCIE = 1; // Enable guard time count match interrupt

U1SCINTbits.WTCIF = 0; // Clear WTC interrupt flag

U1SCINTbits.WTCIE = 1; // Enable wait time count match interrupt

U1SCINTbits.TXRPTIF = 0; // Clear TX repeat error interrupt flag (Optional)

U1SCINTbits.TXRPTIE = 1; // Enable TX repeat error interrupt (Optional)

U1SCINTbits.RXRPTIF = 0; // Clear TX repeat error interrupt flag (Optional)

U1SCINTbits.RXRPTIE = 1; // Enable RX repeat error interrupt (Optional)

U1STAbits.PERR = 0; // Clear Parity error flag (Optional)

U1SCINTbits.PARIE = 1; // Enable RX parity error interrupt (Optional)

// UART 1 Error interrupt

IPC16bits.U1ERIP = 5; // Error interrupt priority

IFS4bits.U1ERIF = 0; // Clear U1 error flag

IEC4bits.U1ERIE = 1; // Enable error interrupts

 2009-2013 Microchip Technology Inc. DS70000582E-page 49

UART

15.5.2 POST-Answer-To-Reset (ATR) INITIALIZATION

After the terminal has done a reset of the Smart Card and received the setup parameters

contained in the ATR, the user software can configure the module for communication as follows:

1. Disable the UART for configuration changes by clearing the UARTEN bit.

2. Set the PTRCL (UxSCCON<1>), T0PD (UxSCCON<2>), CONV (UxSCCON<3>) and

TXRPT<1:0> bits (UxSCCON<5:4>) according to ATR parameters.

3. Program the UxBRG register for the ETU defined in ATR.

4. Program the UxGTC register and set GTCIE (UxSCINT<0>).

5. Program UxWTCL/H registers and set WTCIE (UxSCINT<1>).

6. Enable interrupts as described in Section 7.3 “Receive Interrupt”, Section 15.2 “Smart

Card Control Registers” and Section 15.4 “Smart Card Interrupt Configuration”.

7. Clear the URXEN bit.

8. Enable the UART by setting the UARTEN bit.

9. Set the UTXEN bit (UxSTA<10>) to start the first transmission to the Smart Card.

Example 15-2: Smart Card Initialization Code for UART1

15.5.3 T = 0 PROTOCOL COMMUNICATION

Transmission with T = 0:

1. Set URXEN to ‘0’ and UTXEN to ‘1’.

2. Write data into UxTXREG.

3. Take appropriate actions according to the ISO 7816 standard if the WTCIF, GTCIF and/or

TXRPTIF bits are set.

4. Set LAST = 1 (UxTXREG<15>) for the last byte of data.

Reception with T =

1. Set UTXEN to ‘0’ and URXEN to ‘1’.

2. Read the UxRXREG as the data becomes available upon the receive interrupt.

3. Take appropriate actions according to the ISO 7816 standard if the WTCIF, GTCIF and/or

RXRPTIF bits are set.

Note: Only one enable bit (UTXEN or URXEN) can be set at any given time.

// Smart card initialization code example for UART1

U1BRG = 25; // Set bit rate

U1MODEbits.PDSEL = 0x01; // 8 bits, even parity

// Smart card specific register configuration

U1SCCONbits.SCEN = 1; // Enable Smart card mode

U1SCCONbits.PTRCL = 0; // T=0 protocol

U1SCCONbits.T0PD = 0; // 1 ETU pull down duration

U1SCCONbits.CONV = 0; // Direct logic convention

U1SCCONbits.TXRPT = 1; // Retransmit error byte 2 times

U1GTC = 0x0012; // Guard time = 12 ETU

U1WTCL = 0x0022; // Wait time = 22 ETU

U1WTCH = 0x0000;

U1MODEbits.UARTEN = 1; // Enable UART

Note: Due to the TX and RX pins being shorted, a receive interrupt will be generated on

transmission of a character, if enabled. It is recommended to disable receive

interrupts when transmitting.

Note: For the last character, the user must ensure that the guard time is satisfied before

transmitting the response. The GTC may be used for this purpose, whereas the

WTC interrupt may be disabled or ignored.

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 50  2009-2013 Microchip Technology Inc.

15.5.4 T = 1 PROTOCOL COMMUNICATION

Transmission with T = 1:

1. Set URXEN to ‘0’ and UTXEN to ‘1’.

2. Write data into UxTXREG.

3. Program the value of BWT to UxWTCL/H and set WTCIE (UxSCINT<1>) to ‘1’.

4. Take appropriate actions according to the ISO 7816 standard if the WTCIF, GTCIF and/or

TXRPTIF bits are set.

5. Set the LAST = 1 bit (UxTXREG<15>) for the last byte of data.

Reception with T = 1:

1. Set UTXEN to ‘0’ and URXEN to ‘1’.

2. Read the UxRXREG as the data becomes available upon the receive interrupt.

3. Program the value of CWT to UxWTCL/H and set WTCIE (UxSCINT<1>) to ‘1’.

4. Take appropriate actions according to the ISO 7816 standard if the WTCIF, GTCIF and/or

RXRPTIF bits are set.

Note: For the last character, the user must ensure the guard time is satisfied before trans-

mitting the response. The GTC may be used for this purpose, whereas the WTC

interrupt may be disabled or ignored.

 2009-2013 Microchip Technology Inc. DS70000582E-page 51

UART

16.0 REGISTERS MAP

A summary of the registers associated with the UART module of the dsPIC33 and PIC24 device families is provided in Tab le 1 6 -1 .

Table 16-1: Registers Associated with UARTx

(1)

SFR Name Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

All

Resets

UxMODE UARTEN — USIDL IREN RTSMD ALTIO UEN1 UEN0 WAKE LPBACK ABAUD URXINV BRGH PDSEL1 PDSEL0 STSEL

0000

UxSTA UTXISEL1 UTXINV UTXISEL0 URXEN UTXBRK UTXEN UTXBF TRMT URXISEL1 URXISEL0 ADDEN RIDLE PERR FERR OERR URXDA

0110

UxADMD ADM_MASK7 ADM_MASK6 ADM_MASK5 ADM_MASK4 ADM_MASK3 ADM_MASK2 ADM_MASK1 ADM_MASK0 ADM_ADDR7 ADM_ADDR6 ADM_ADDR5 ADM_ADDR4 ADM_ADDR3 ADM_ADDR2 ADM_ADDR1 ADM_ADDR0

0000

UxTXREG LAST — — — — — — UTX8 UARTx Transmit Register

xxxx

UxRXREG — — — — — — — URX8 UARTx Receive Register

0000

UxBRG Baud Rate Generator Prescaler Register

0000

UxSCCON — — — — — — — — — —TXRPT1

(2)

TXRPT0

(2)

CONV T0PD

(2)

PTRCL SCEN

0000

UxSCINT — —RXRPTIF

(2)

TXRPTIF

(2)

— —WTCIFGTCIF — PARIE RXRPTIE TXRPTIE — —WTCIEGTCIE

0000

UxGTC — — — — — — — GTC8 GTC7 GTC6 GTC5 GTC4 GTC3 GTC2 GTC1 GTC0

0000

UxWTCL WTC15 WTC14 WTC13 WTC12 WTC11 WTC10 WTC9 WTC8 WTC7 WTC6 WTC5 WTC4 WTC3 WTC2 WTC1 WTC0

0000

UxWTCH — — — — — — — — WTC23 WTC22 WTC21 WTC20 WTC19 WTC18 WTC17 WTC16

0000

Legend:

= unknown value on Reset, — = unimplemented, read as ‘

’. Reset values are shown in hexadecimal.

Note 1:

The registers associated with UARTx are shown for reference. Refer to the

“Universal Asynchronous Receiver Transmitter (UART)”

chapter of the specific device data sheet for the registers associated with other UART modules.

These bits are applicable to T =

only. See the PTRCL bit (UxSCCON<1>).

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 52  2009-2013 Microchip Technology Inc.

17.0 RELATED APPLICATION NOTES

This section lists application notes that are related to this section of the manual. These applica-

tion notes may not be written specifically for the dsPIC33 and PIC24 device families, but the

concepts are pertinent and could be used with modification and possible limitations. The current

application notes related to the UART module include the following:

Title Application Note #

Smart Card Communication Using PIC

MCUs AN1370

Note: Please visit the Microchip web site (www.microchip.com) for additional application

notes and code examples for the dsPIC33 and PIC24 families of devices.

 2009-2013 Microchip Technology Inc. DS70000582E-page 53

UART

18.0 REVISION HISTORY

Revision A (January 2009)

This is the initial released version of the document.

Revision B (July 2010)

This revision includes the following changes:

• Changed the document name from dsPIC33E Family Reference Manual to dsPIC33E/

PIC24E Family Reference Manual

• Deleted watermark from the code examples

• Added Note 3 in the note box in Section 11.2 “UART Operation in Idle Mode”

• Updated and added a note to Figure 7-2

• Updated Figure 8-1

• Added Figure 10-1

• Changed the bit 8 characteristic from W-x to R/W-0 in Register 2-6

• Minor changes to the text and formatting have been incorporated throughout the document

Revision C (December 2011)

This revision includes the following updates:

• Updated the baud rate feature values and the hardware flow control option in Section 1.0

“Introduction”

• Relocated the note box originally located in 17.1 “Introduction” to Section 2.0 “Control

Registers”

• Changed all occurrences of the instruction cycle clock frequency (F

CY) to: FP

• Changed all occurrences of Low-Speed mode to: Standard-Speed mode

• Added Note 2 and updated the bit value definitions for BRGH in UxMODE: UARTx Mode

• Updated the UART Transmission with Interrupts (see Example 5-1)

• Updated the UART Receive Only with Polling (Interrupts Disabled) (see Example 7-1)

• Updated the UART Reception and Transmission with DMA (see Example 7-1)

• Added a note box to Section 12.0 “Operation of UxCTS and UxRTS Control Pins”

• Removed 17.16 “Design Tips”

• Minor updates to text and formatting were incorporated throughout the document

Revision D (April 2012)

This revision includes the following updates:

• Added a note to Section 7.0 “UART Receiver”

• Added a note to Section 14.0 “LIN/J2602 Support”

• Additional minor updates to text and formatting were incorporated throughout the document

Revision E (October 2013)

This revision includes the following updates:

• Name of Family Reference Manual has been changed to “dsPIC33/PIC24 Family

Reference Manual”

• Section number has been removed from the title

• Side tabs with section numbers have been removed

• Added Smart Card Communication section

• Additional minor updates to text and formatting were incorporated throughout the document

dsPIC33/PIC24 Family Reference Manual

DS70000582E-page 54  2009-2013 Microchip Technology Inc.

NOTES:

 2009-2013 Microchip Technology Inc. DS70000582E-page 55

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ISBN: 978-1-62077-507-3

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Fax: 774-760-0088

Chicago

Itasca, IL

Tel: 630-285-0071

Fax: 630-285-0075

Cleveland

Independence, OH

Tel: 216-447-0464

Fax: 216-447-0643

Dallas

Addison, TX

Tel: 972-818-7423

Fax: 972-818-2924

Detroit

Farmington Hills, MI

Tel: 248-538-2250

Fax: 248-538-2260

Indianapolis

Noblesville, IN

Tel: 317-773-8323

Fax: 317-773-5453

Los Angeles

Mission Viejo, CA

Tel: 949-462-9523

Fax: 949-462-9608

Santa Clara

Santa Clara, CA

Tel: 408-961-6444

Fax: 408-961-6445

Toronto

Mississauga, Ontario,

Canada

Tel: 905-673-0699

Fax: 905-673-6509

ASIA/PACIFIC

Asia Pacific Office

Suites 3707-14, 37th Floor

Tower 6, The Gateway

Harbour City, Kowloon

Hong Kong

Tel: 852-2401-1200

Fax: 852-2401-3431

Australia - Sydney

Tel: 61-2-9868-6733

Fax: 61-2-9868-6755

China - Beijing

Tel: 86-10-8569-7000

Fax: 86-10-8528-2104

China - Chengdu

Tel: 86-28-8665-5511

Fax: 86-28-8665-7889

China - Chongqing

Tel: 86-23-8980-9588

Fax: 86-23-8980-9500

China - Hangzhou

Tel: 86-571-2819-3187

Fax: 86-571-2819-3189

China - Hong Kong SAR

Tel: 852-2943-5100

Fax: 852-2401-3431

China - Nanjing

Tel: 86-25-8473-2460

Fax: 86-25-8473-2470

China - Qingdao

Tel: 86-532-8502-7355

Fax: 86-532-8502-7205

China - Shanghai

Tel: 86-21-5407-5533

Fax: 86-21-5407-5066

China - Shenyang

Tel: 86-24-2334-2829

Fax: 86-24-2334-2393

China - Shenzhen

Tel: 86-755-8864-2200

Fax: 86-755-8203-1760

China - Wuhan

Tel: 86-27-5980-5300

Fax: 86-27-5980-5118

China - Xian

Tel: 86-29-8833-7252

Fax: 86-29-8833-7256

China - Xiamen

Tel: 86-592-2388138

Fax: 86-592-2388130

China - Zhuhai

Tel: 86-756-3210040

Fax: 86-756-3210049

ASIA/PACIFIC

India - Bangalore

Tel: 91-80-3090-4444

Fax: 91-80-3090-4123

India - New Delhi

Tel: 91-11-4160-8631

Fax: 91-11-4160-8632

India - Pune

Tel: 91-20-3019-1500

Japan - Osaka

Tel: 81-6-6152-7160

Fax: 81-6-6152-9310

Japan - Tokyo

Tel: 81-3-6880- 3770

Fax: 81-3-6880-3771

Korea - Daegu

Tel: 82-53-744-4301

Fax: 82-53-744-4302

Korea - Seoul

Tel: 82-2-554-7200

Fax: 82-2-558-5932 or

82-2-558-5934

Malaysia - Kuala Lumpur

Tel: 60-3-6201-9857

Fax: 60-3-6201-9859

Malaysia - Penang

Tel: 60-4-227-8870

Fax: 60-4-227-4068

Philippines - Manila

Tel: 63-2-634-9065

Fax: 63-2-634-9069

Singapore

Tel: 65-6334-8870

Fax: 65-6334-8850

Taiwan - Hsin Chu

Tel: 886-3-5778-366

Fax: 886-3-5770-955

Taiwan - Kaohsiung

Tel: 886-7-213-7828

Fax: 886-7-330-9305

Taiwan - Taipei

Tel: 886-2-2508-8600

Fax: 886-2-2508-0102

Thailand - Bangkok

Tel: 66-2-694-1351

Fax: 66-2-694-1350

EUROPE

Austria - Wels

Tel: 43-7242-2244-39

Fax: 43-7242-2244-393

Denmark - Copenhagen

Tel: 45-4450-2828

Fax: 45-4485-2829

France - Paris

Tel: 33-1-69-53-63-20

Fax: 33-1-69-30-90-79

Germany - Munich

Tel: 49-89-627-144-0

Fax: 49-89-627-144-44

Italy - Milan

Tel: 39-0331-742611

Fax: 39-0331-466781

Netherlands - Drunen

Tel: 31-416-690399

Fax: 31-416-690340

Spain - Madrid

Tel: 34-91-708-08-90

Fax: 34-91-708-08-91

UK - Wokingham

Tel: 44-118-921-5869

Fax: 44-118-921-5820

Worldwide Sales and Service

08/20/13