PIC18F258 Datasheet, PDF (227/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN

PIC18FXX8
FIGURE 19-3:
TRANSMIT MESSAGE FLOW CHART
Start
No
Are any
TXREQ
bits = 1
?
Yes
Clear: TXABT, TXLARB
and TXERR
The message transmission sequence begins when
the device determines that the TXREQ for any of the
transmit registers has been set.
Clearing the TXREQ bit while it is set, or setting
the ABAT bit before the message has started
transmission, will abort the message.
Is
CAN bus Available
No
to Start Transmission
?
Yes
Examine TXPRI <1:0> to
Determine Highest Priority Message
Begin Transmission (SOF)
No
Is
Yes
TXREQ = 0
ABAT = 1
?
Was
No
Message Transmitted
Successfully?
Set
TXERR = 1
Yes
Set TXREQ = 0
Is
TXLARB = 1?
Yes
Generate
Interrupt
Is
TXIE = 1?
No
Set
TXBUFE = 1
The TXIE bit determines if an inter-
rupt should be generated when a
message is successfully transmitted.
A message can also be
aborted, if a message
error or lost arbitration
condition occurred during
transmission.
No
Is
TXREQ = 0
or TXABT = 1
?
No
Yes _{Arbitration Lost During}
Transmission
Yes
Abort Transmission:
Set TXABT = 1
END
 2002 Microchip Technology Inc.
Preliminary
DS41159B-page 225