Datasheet

PIC18F66K80 FAMILY
DS39977F-page 442  2010-2012 Microchip Technology Inc.
27.6.3 TRANSMIT PRIORITY
Transmit priority is a prioritization within the
PIC18F66K80 family devices of the pending transmitta-
ble 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 buf-
fers 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 buffer has
the highest possible priority. If the TXP bits for a partic-
ular message buffer are set to ‘
00’, that buffer has the
lowest possible priority.
FIGURE 27-2: 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