PIC18F258-ESLASHLSQTP datasheet(230/402 Pages) MICROCHIP

230 / 402 page

PIC18FXX8

DS41159E-page 228

19.4.3

INITIATING TRANSMISSION

To initiate message transmission, the TXREQ bit must

be set for each buffer to be transmitted. When TXREQ

is set, the TXABT, TXLARB and TXERR bits will be

cleared.

Setting the TXREQ bit does not initiate a message

transmission; it merely flags a message buffer as ready

for transmission. Transmission will start when the

device detects that the bus is available. The device will

then begin transmission of the highest priority message

that is ready.

When the transmission has completed successfully,

the TXREQ bit will be cleared, the TXBnIF bit will be set

and an interrupt will be generated if the TXBnIE bit is

set.

If the message transmission fails, the TXREQ will

remain set, indicating that the message is still pending

for transmission and one of the following condition flags

will be set. If the message started to transmit but

encountered an error condition, the TXERR and the

IRXIF bits will be set and an interrupt will be generated.

If the message lost arbitration, the TXLARB bit will be

set.

19.4.4

ABORTING TRANSMISSION

The MCU can request to abort a message by clearing

the TXREQ bit associated with the corresponding

message buffer (TXBnCON<3>). Setting the ABAT bit

(CANCON<4>) will request an abort of all pending

messages. If the message has not yet started transmis-

sion, or if the message started but is interrupted by loss

of arbitration or an error, the abort will be processed.

The abort is indicated when the module sets the ABT

bits for the corresponding buffer (TXBnCON<6>). If the

message has started to transmit, it will attempt to

transmit the current message fully. If the current

message is transmitted fully and is not lost to arbitration

or an error, the ABT bit will not be set because the

message was transmitted successfully. Likewise, if a

message is being transmitted during an abort request

and the message is lost to arbitration or an error, the

message will not be retransmitted and the ABT bit will

be set, indicating that the message was successfully

aborted.

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