Datasheet

PIC18F2682/2685/4682/4685

EXAMPLE 23-4: TRANSMITTING A CAN MESSAGE USING WIN BITS

; Need to transmit Standard Identifier message 123h using TXB0 buffer.

; To successfully transmit, CAN module must be either in Normal or Loopback mode.

; TXB0 buffer is not in access bank. Use WIN bits to map it to RXB0 area.

MOVF CANCON, W ; WIN bits are in lower 4 bits only. Read CANCON

; register to preserve all other bits. If operation

; mode is already known, there is no need to preserve

; other bits.

ANDLW B’11110000’ ; Clear WIN bits.

IORLW B’00001000’ ; Select Transmit Buffer 0

MOVWF CANCON ; Apply the changes.

; Now TXB0 is mapped in place of RXB0. All future access to RXB0 registers will actually

; yield TXB0 register values.

; Load transmit data into TXB0 buffer.

MOVLW MY_DATA_BYTE1 ; Load first data byte into buffer

MOVWF RXB0D0 ; Access TXB0D0 via RXB0D0 address.

; Load rest of the data bytes - up to 8 bytes into “TXB0” buffer using RXB0 registers.

...

; Load message identifier

MOVLW 60H ; Load SID2:SID0, EXIDE = 0

MOVWF RXB0SIDL

MOVLW 24H ; Load SID10:SID3

MOVWF RXB0SIDH

; No need to load RXB0EIDL:RXB0EIDH, as we are transmitting Standard Identifier Message only.

; Now that all data bytes are loaded, mark it for transmission.

MOVLW B’00001000’ ; Normal priority; Request transmission

MOVWF RXB0CON

; If required, wait for message to get transmitted

BTFSC RXB0CON, TXREQ ; Is it transmitted?

BRA $-2 ; No. Continue to wait...

; Message is transmitted.

; If required, reset the WIN bits to default state.