Inter-Integrated Circuit (I2C) Interface - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 557

After the HCS12 initializes the current time and calendar information, the DS1307 will inter-
rupt the HCS12 periodically (most commonly, once per second) so that the HCS12 can update
the time display periodically.

Example 11.3
▼

Write a function to configure the DS1307 to operate with the following setting:
• SQWOUT output enabled
• SQWOUT output set to 1 Hz
• SQWOUT idle high when it is disabled
Solution: The user needs to send the following bytes to the DS1307:
• Address byte $D0 (bit 0 is 0 to select write operation)
• Register address $07
• Control byte $90 (passed in accumulator B)
The following function will confi gure the DS1307 accordingly:
openDS1307 ldaa #$D0 ; place DS1307 ID in A

jsr sendSlaveID

brclr IBSR,RXAK,sndRegAdr ; did DS1307 acknowledge?

ldab #$FF ; return 2 1 as error code

rts

sndRegAdr movb #$07,IBDR ; send out the control register address

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

movb #IBIF,IBSR ; clear the IBIF flag

brclr IBSR,RXAK,sndok ; did DS1307 acknowledge?

ldab #$FF

rts

sndok stab IBDR ; send out control byte

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

movb #IBIF,IBSR

bclr IBCR,MSSL ; generate stop condition

rts
The same confi guration can be performed by the following C function:
char openDS1307(char ctrl)
{

sendSlaveID(0xD0); /* send out DS1307's ID */

if (IBSR & RXAK) /* if DS1307 did not acknowledge, send error code */

return 2 1;

IBDR 5 0x07; /* send out control register address */

while(!(IBSR & IBIF));

IBSR 5 IBIF; /* clear IBIF flag */

if (IBSR & RXAK) /* if DS1307 did not acknowledge, send error code */

return 2 1;

IBDR 5 ctrl; /* send out control byte */

while(!(IBSR & IBIF));

IBSR 5 IBIF;