Datasheet

Table Of Contents
PIC18F2480/2580/4480/4580
DS39637D-page 334 © 2009 Microchip Technology Inc.
24.6.3 TRANSMIT PRIORITY
Transmit priority is a prioritization within the
PIC18F2480/2580/4480/4580 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 Start-Of-Frame (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 the TXP bits
for a particular message buffer are set to ‘11’, that buf-
fer has the highest possible priority. If the TXP bits for
a particular message buffer are set to ‘00’, that buffer
has the lowest possible priority.
FIGURE 24-2: 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