Inter-Integrated Circuit (I2C) Interface - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 577

IBCR | 5 TXAK; /* prepare to send NACK */

temp 5 IBDR; /* a dummy read to trigger nine clock pulses */

while(!(IBSR & IBIF));
IBSR 5 IBIF;

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

return IBDR;
}

▲

Example 11.14
▼

Write a subroutine to read the converted temperature and return the upper and lower bytes
in double accumulator D. Assume that the temperature conversion has been started but this
function needs to make sure that the converted temperature value is a result of the most recent
Start Convert T command.
Solution: This subroutine calls the previous subroutine to make sure that the DONE bit is set
to 1 and reads the converted temperature from the DS1631A. The assembly subroutine is as
follows:
readTemp ldx #0 ; initialize return error code

rdLoop jsr readConf ; is temperature conversion done yet?

cmpb # 2 1 ; is there any error?

beq rdErr ; “

andb #$80 ; check DONE bit

bpl rdLoop ; conversion not done yet?

ldaa #$92 ; generate a start condition and send out

jsr sendSlaveID ; the DS1631A ID

brclr IBSR,RXAK,rdTempok1 ; did DS1631A acknowledge?

ldx # 2 1

rts

rdTempok1 movb #$AA,IBDR ; sends Read-Temperature command

brclr IBSR,IBIF,* ;

movb #IBIF,IBSR

brclr IBSR,RXAK,rdTempok2 ; did DS1631A acknowledge?

ldx # 2 1

rts

rdTempok2 bset IBCR,RSTA ; generate a restart condition

movb #$93,IBDR ; send DS1631A's ID with R/W set to 1

brclr IBSR,IBIF,*

movb #IBIF,IBSR

brclr IBSR,RXAK,rdTempok3 ; did DS1631A acknowledge?

ldx # 2 1

rts
rdTempok3 bclr IBCR,TXRX 1 TXAK ; prepare to receive an ACK

ldaa IBDR ; perform a dummy read

brclr IBSR,IBIF,* ; wait for high byte of temperature to shift in

movb #IBIF,IBSR

bset IBCR,TXAK ; prepare to send NACK for the last read