Controller Area Network (CAN) - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 679

tb0 movb #0,tbuf,sp ; mark transmit buffer 0 empty

bra tcopy

tb1 movb #1,tbuf,sp ; mark transmit buffer 1 empty

bra tcopy

tb2 movb #2,tbuf,sp ; mark transmit buffer 2 empty

tcopy movb CAN1TFLG,CAN1TBSEL ; make the empty transmit buffer accessible

ldy #CAN1TIDR0 ; set y to point to the start of the transmit buffer

ldab #7 ; always copy seven words (place word count in B)

cploop movw 2,x 1 ,2,y 1

dbne b,cploop

ldab tbuf,sp

cmpb #0

beq istb0

cmpb #1

beq istb1

movb #$04,CAN1TFLG ; mark buffer 2 ready for transmission

bra dcopy

istb0 movb #$01,CAN1TFLG ; mark buffer 0 ready for transmission

bra dcopy

istb1 movb #$02,CAN1TFLG ; mark buffer 1 ready for transmission

dcopy leas 1,sp ; deallocate local variables

pulb
puly
rts
The C language version of the function is as follows:
void snd2can1(char *ptr)
{

int tb,i,*pt1,*pt2;

pt1 5 (int *)ptr; /* convert to integer pointer */

while(1) { /* find an empty transmit buffer */

if(CAN1TFLG & 0x01){

tb 5 0;

break;

}

if(CAN1TFLG & 0x02){

tb 5 1;

break;

}

if(CAN1TFLG & 0x04){

tb 5 2;

break;

}

}

CAN1TBSEL 5 CAN1TFLG; /* make empty transmit buffer accessible */

pt2 5 (int *)&CAN1TIDR0; /* pt2 points to the IDR0 of TXFG */

for (i 5 0; i < 7; i 11 ) /* copy the whole transmit buffer */

*pt2 11 5 *pt1 11 ;