MC68HC12 Datasheet, PDF (320/478 Pages) Motorola, Inc – The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit

Inter IC Bus
monitor the IBIF bit rather than the TCF bit since their operation is
different when arbitration is lost.
Note that when an interrupt occurs at the end of the address cycle the
master will always be in transmit mode, i.e. the address is transmitted. If
master receive mode is required, indicated by R/W bit in IBDR, then the
Tx/Rx bit should be toggled at this stage.
During slave mode address cycles (IAAS=1) the SRW bit in the status
register is read to determine the direction of the subsequent transfer and
the Tx/Rx bit is programmed accordingly. For slave mode data cycles
(IAAS=0) the SRW bit is not valid, the Tx/Rx bit in the control register
should be read to determine the direction of the current transfer.
The following is an example of a software response by a 'master
transmitter' in the interrupt routine (see Figure 17-4).
ISR
TRANSMIT
BCLR
BRCLR
BRCLR
BRSET
MOVB
IBSR,#$02
IBCR,#$20,SLAVE
IBCR,#$10,RECEIVE
IBSR,#$01,END
DATABUF,IBDR
;CLEAR THE IBIF FLAG
;BRANCH IF IN SLAVE MODE
;BRANCH IF IN RECEIVE MODE
;IF NO ACK, END OF TRANSMISSION
;TRANSMIT NEXT BYTE OF DATA
17.7.4 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.
MASTX
END
EMASTX
TST
BEQ
BRSET
MOVB
DEC
BRA
BCLR
RTI
TXCNT
END
IBSR,#$01,END
DATABUF,IBDR
TXCNT
EMASTX
IBCR,#$20
;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
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
Technical Data
320
Inter IC Bus
MC68HC912DT128A — Rev 4.0
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