Datasheet

PIC18F2585/2680/4585/4680
DS39625C-page 328 Preliminary © 2007 Microchip Technology Inc.
23.6.3 TRANSMIT PRIORITY
Transmit priority is a prioritization within the
PIC18F2585/2680/4585/4680 devices of the pending
transmittable messages. This is independent from and
not related to any prioritization implicit in the message
arbitration scheme built into the CAN protocol. Prior to
sending the SOF, the priority of all buffers that are
queued for transmission is compared. The transmit
buffer with the highest priority will be sent first. If two
buffers have the same priority setting, the buffer with
the highest buffer number will be sent first. There are
four levels of transmit priority. If TXP bits for a particular
message buffer are set to ‘11’, that buffer has the high-
est possible priority. If TXP bits for a particular message
buffer are set to ‘00’, that buffer has the lowest possible
priority.
FIGURE 23-2: TRANSMIT BUFFERS
TXREQ
TXB0
TXABT TXLARB TXERR TXB0IF MESSAGE
Message
Queue
Control
Transmit Byte Sequencer
TXREQ
TXB1
TXABT TXLARB TXERR TXB1IF MESSAGE TXREQ
TXB2
TXABT TXLARB TXERR TXB2IF MESSAGE MESSAGE TXB2IF TXREQ TXABT TXLARB TXERR
TXB3 - TXB8