SC312XDP512F0MPVR datasheet(415/1348 Pages) FREESCALE

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Chapter 9 Inter-Integrated Circuit (IICV2) Block Description

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

415

9.7.1.4

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.

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.

9.7.1.5

Generation of Repeated START

At the end of data transfer, if the master continues to want 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.

9.7.1.6

Slave Mode

In the slave interrupt service routine, the module addressed as slave bit (IAAS) should be tested to check

if a calling of its own address has just been received. If IAAS is set, software should set the transmit/receive

mode select bit (Tx/Rx bit of IBCR) according to the R/W command bit (SRW). Writing to the IBCR

clears the IAAS automatically. Note that the only time IAAS is read as set is from the interrupt at the end

of the address cycle where an address match occurred, interrupts resulting from subsequent data transfers

will have IAAS cleared. A data transfer may now be initiated by writing information to IBDR, for slave

transmits, or dummy reading from IBDR, in slave receive mode. The slave will drive SCL low in-between

byte transfers, SCL is released when the IBDR is accessed in the required mode.

MASTX

TST

TXCNT

;GET VALUE FROM THE TRANSMITING COUNTER

BEQ

END

;END IF NO MORE DATA

BRSET

IBSR,#$01,END

;END IF NO ACK

MOVB

DATABUF,IBDR

;TRANSMIT NEXT BYTE OF DATA

DEC

TXCNT

;DECREASE THE TXCNT

BRA

EMASTX

;EXIT

END

BCLR

IBCR,#$20

;GENERATE A STOP CONDITION

EMASTX

RTI

;RETURN FROM INTERRUPT

MASR

DEC

RXCNT

;DECREASE THE RXCNT

BEQ

ENMASR

;LAST BYTE TO BE READ

MOVB

RXCNT,D1

;CHECK SECOND LAST BYTE

DEC

;TO BE READ

BNE

NXMAR

;NOT LAST OR SECOND LAST

LAMAR

BSET

IBCR,#$08

;SECOND LAST, DISABLE ACK

;TRANSMITTING

BRA

NXMAR

ENMASR

BCLR

IBCR,#$20

;LAST ONE, GENERATE ‘STOP’ SIGNAL

NXMAR

MOVB

IBDR,RXBUF

;READ DATA AND STORE

RTI

RESTART

BSET

IBCR,#$04

;ANOTHER START (RESTART)

MOVB

CALLING,IBDR

;TRANSMIT THE CALLING ADDRESS;D0=R/W

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