INTEDG datasheet(317/478 Pages) MICROCHIP

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DS41414D-page 317

PIC16(L)F1946/47

25.4.4

BREAK CHARACTER SEQUENCE

The EUSART module has the capability of sending the

special Break character sequences that are required by

the LIN bus standard. A Break character consists of a

Start bit, followed by 12 ‘0’ bits and a Stop bit.

To send a Break character, set the SENDB and TXEN

bits of the TXxSTA register. The Break character trans-

mission is then initiated by a write to the TXxREG. The

value of data written to TXxREG will be ignored and all

‘0’s will be transmitted.

The SENDB bit is automatically reset by hardware after

the corresponding Stop bit is sent. This allows the user

to preload the transmit FIFO with the next transmit byte

following the Break character (typically, the Sync

character in the LIN specification).

The TRMT bit of the TXxSTA register indicates when the

transmit operation is active or Idle, just as it does during

normal transmission. See Figure 25-9 for the timing of

the Break character sequence.

25.4.4.1

Break and Sync Transmit Sequence

The following sequence will start a message frame

header made up of a Break, followed by an auto-baud

Sync byte. This sequence is typical of a LIN bus

master.

Configure the EUSART for the desired mode.

Set the TXEN and SENDB bits to enable the

Break sequence.

Load the TXxREG with a dummy character to

initiate transmission (the value is ignored).

Write ‘55h’ to TXxREG to load the Sync charac-

ter into the transmit FIFO buffer.

After the Break has been sent, the SENDB bit is

reset by hardware and the Sync character is

then transmitted.

When the TXxREG becomes empty, as indicated by

the TXxIF, the next data byte can be written to TXxREG.

25.4.5

RECEIVING A BREAK CHARACTER

The Enhanced EUSART module can receive a Break

character in two ways.

The first method to detect a Break character uses the

FERR bit of the RCxSTA register and the Received

data as indicated by RCxREG. The Baud Rate

Generator is assumed to have been initialized to the

expected baud rate.

A Break character has been received when;

• RCxIF bit is set

• FERR bit is set

• RCxREG = 00h

The second method uses the Auto-Wake-up feature

described in Section 25.4.3 “Auto-Wake-up on

Break”. By enabling this feature, the EUSART will

sample the next two transitions on RXx/DTx, cause an

RCxIF interrupt, and receive the next data byte

followed by another interrupt.

Note that following a Break character, the user will

typically want to enable the Auto-Baud Detect feature.

For both methods, the user can set the ABDEN bit of

the BAUDxCON register before placing the EUSART in

Sleep mode.

FIGURE 25-9:

SEND BREAK CHARACTER SEQUENCE

Write to TXxREG

Dummy Write

BRG Output

(Shift Clock)

Start bit

bit 0

bit 1

bit 11

Stop bit

Break

TXxIF bit

(Transmit

interrupt Flag)

TXx/CKx (pin)

TRMT bit

(Transmit Shift

Reg. Empty Flag)

SENDB

(send Break

control bit)

SENDB Sampled Here

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