Inter-Integrated Circuit (I2C) Interface - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 586

IBDR 5 addr; /* send out starting address of pagewrite */

while(!(IBSR & IBIF)); /* wait until the address is shifted out */

IBSR 5 IBIF; /* clear IBIF flag */

if (IBSR & RXAK)

return 2 1; /* return 2 1 if EEPROM did not respond */

while(ByteCnt) {

IBDR 5 *ptr 11 ; /* send out 1 byte of data */

while(!(IBSR & IBIF));

IBSR 5 IBIF;

if (IBSR & RXAK)

return 2 1; /* return 2 1 if EEPROM did not respond */

ByteCnt 22 ;

}

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

return 0;

}

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In some applications, the program may need to write several blocks of data to different
locations. An internal write cycle takes about 5 ms to complete. The designer can either call
a delay function to wait for 5 ms or use acknowledge polling to find out whether the internal
write has completed.

Example 11.18
▼

Write a C function to implement the algorithm described in Figure 11.38.
Solution: The function eeAckPoll() will poll the EEPROM until it is not busy.
void eeAckPoll(char ID)
{

SendSlaveID(ID);

while(IBSR & RXAK){

IBCR | 5 RSTA; /* generate a restart condition */

IBDR 5 ID; /* send out EEPROM ID */

while(!(IBSR & IBIF));

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

} ; /* continue if EEPROM did not acknowledge */

IBCR & 5 , MSSL; /* generate a stop condition 2 indispensable */

}

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11.9 Summary

The I 2 C protocol is an alternative to the SPI serial interface protocol. Compared with the
SPI protocol, the I 2 C bus offers the following advantages:
• No chip-enable or chip-select signal for selecting slave devices
• Allows multiple master devices to coexist in a system because it provides easy bus
arbitration