Inter-Integrated Circuit (I2C) Interface - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 584

Example 11.16
▼

Write a subroutine that writes a byte into the 24LC08B. The device ID, memory address,
and data to be written are passed to this routine in the stack.
Solution: The assembly subroutine that writes a byte into the 24LC08B to the specified address
is as follows:
EE_ID equ 5 ; stack offset for EE_ID

EE_addr equ 4 ; stack offset for EE_addr

EE_dat equ 3 ; stack offset for EE_data

EEbyteWrite psha

ldaa EE_ID,sp ; get the EEPROM ID from stack

jsr sendSlaveID ; generate start condition, send EEPROM ID

brclr IBSR,RXAK,bywriteok1 ; does EEPROM acknowledge?

ldab #$FF ; return 2 1 as the error code

pula

rts

bywriteok1 ldaa EE_addr,sp ; get the address to be accessed from the stack

staa IBDR ; send address to I2C bus

brclr IBSR,IBIF,* ; wait until address is shifted out

movb #IBIF,IBSR ; clear the IBIF flag

brclr IBSR,RXAK,bywriteok2 ; does EEPROM acknowledge?

ldab #$FF ; return 2 1 as the error code

pula

rts

bywriteok2 ldaa EE_dat,sp ; get the data byte to be written from stack

staa IBDR ; send out the data byte

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

movb #IBIF,IBSR ; clear the IBIF flag

brclr IBSR,RXAK,bywriteok3 ; does EEPROM acknowledge?

ldab #$FF ; return 2 1 as the error code

pula

rts

bywriteok3 bclr IBCR,MSSL ; generate stop condition

ldab #0 ; return error code 0

pula
rts
The C language version of the function is as follows:
char EEbyteWrite(char ID, char addr, char data)
{

SendSlaveID(ID);

if (IBSR & RXAK) /* error if EEPROM does not respond */

return 2 1;

IBDR 5 addr; /* send out address of the location to be written */

while(!(IBSR & IBIF));

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

if (IBSR & RXAK) /* error if EEPROM does not respond */

return 2 1;

IBDR 5 data; /* send out the data byte */