Inter-IC Bus
IIC Programming Examples
68HC(9)12DG128 Rev 1.0
MOTOROLA
Inter-IC Bus
269
19-iicbus
Generation of
STOP
A data transfer ends with a STOP signal generated by the 'master'
device. A master transmitter can simply generate a STOP signal after all
the data has been transmitted. The following is an example showing how
a stop condition is generated by a master transmitter.
If a master receiver wants to terminate a data transfer, it must inform the
slave transmitter by not acknowledging the last byte of data which can
be done by setting the transmit acknowledge bit (TXAK) before reading
the 2nd last byte of data. Before reading the last byte of data, a STOP
signal must be generated first. The following is an example showing how
a STOP signal is generated by a master receiver.
Generation of
Repeated START
At the end of data transfer, if the master still wants to communicate on
the bus, it can generate another START signal followed by another slave
address without first generating a STOP signal. A program example is
as shown.
MASTX
TST
TXCNT
;GET VALUE FROM THE
;TRANSMITING COUNTER
;END IF NO MORE DATA
;END IF NO ACK
;TRANSMIT NEXT BYTE OF DATA
;DECREASE THE TXCNT
;EXIT
;GENERATE A STOP CONDITION
;RETURN FROM INTERRUPT
BEQ
BRSET
MOVB
DEC
BRA
BCLR
RTI
END
IBSR,#$01,END
DATABUF,IBDR
TXCNT
EMASTX
IBCR,#$20
END
EMASTX
MASR
DEC
BEQ
MOVB
DEC
BNE
BSET
RXCNT
ENMASR
RXCNT,D1
D1
NXMAR
IBCR,#$08
;DECREASE THE RXCNT
;LAST BYTE TO BE READ
;CHECK SECOND LAST BYTE
;TO BE READ
;NOT LAST OR SECOND LAST
;SECOND LAST, DISABLE ACK
;TRANSMITTING
LAMAR
BRA
BCLR
MOVB
RTI
NXMAR
IBCR,#$20
IBDR,RXBUF
ENMASR
NXMAR
;LAST ONE, GENERATE ‘STOP’ SIGNAL
;READ DATA AND STORE
RESTART
BSET
MOVB
IBCR,#$04
CALLING,IBDR
ANOTHER START (RESTART)
;TRANSMIT THE CALLING ADDRESS
;D0=R/W