Inter-Integrated Circuit (I2C) Interface - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 573

startOK0 movb #$51,IBDR ; send Start Convert T command

brclr IBSR,IBIF,* ; wait until the byte is shifted out

movb #IBIF,IBSR ; clear the IBIF flag

brclr IBSR,RXAK,startOK1 ; did DS1631A acknowledge?

ldab #$FF

rts

startOK1 bclr IBCR,MSSL ; generate a stop condition

ldab #0 ; normal return code

rts
The C language version of the function is as follows:
char startConv (void)
{

sendSlaveID(0x92); /* generate a start condition and send slave ID */

if (IBSR & RXAK)

return 2 1; /* if not acknowledged, return error code 2 1 */

IBDR 5 0x51; /* send command to start a conversion */

while(!(IBSR & IBIF));

IBSR 5 IBIF; /* clear the IBIF flag */

if (IBSR & RXAK)

return 2 1;

IBCR & 5 , MSSL; /* generate a stop condition */

return 0;

}

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Example 11.12
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Write a function to set the high thermostat temperature. The upper and lower bytes of the
high thermostat temperatures are passed in stack.
Solution: The procedure for setting up the high thermostat temperature is as follows:
Step 1
Assert the start condition and send control byte 0x92 with R/W bit 5 0.
Step 2
Wait until the I 2 C transfer is completed and check to see if the DS1631A acknowledges.
If not, exit.
Step 3
Send an Access TH command to DS1631A.
Step 4
Wait until the I 2 C transfer is completed and check to see if the DS1631A acknowledges.
If not, exit.
Step 5
Send the upper byte of the thermostat temperature to the DS1631A.
Step 6
Wait until the I 2 C transfer is completed and check to see if the DS1631A acknowledges.
If not, exit.