Datasheet

8-12 MCF5407 User’s Manual
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C Programming Examples
BEQ.S RECEIVE;Branch if in receive mode
MOVE.B I2SR,-(A7);Push the address on stack,
BTST.B #0,(A7)+;check ACK from receiver
BNE.B END;If no ACK, end of transmission
TRANSMITMOVE.B DATABUF,-(A7);Stack data byte
MOVE.B (A7)+, I2DR;Transmit next byte of data
8.6.4 Generation of STOP
A data transfer ends when the master signals a STOP, which can occur after all data is sent,
as in the following example.
MASTX MOVE.B I2SR, -(A7);If no ACK, branch to end
BTST.B #0,(A7)+
BNE.B END
MOVE.B TXCNT,D0;Get value from the transmitting counter
BEQ.S END;If no more data, branch to end
MOVE.B DATABUF,-(A7);Transmit next byte of data
MOVE.B (A7)+,I2DR
MOVE.B TXCNT,D0;Decrease the TXCNT
SUBQ.L #1,D0
MOVE.B D0,TXCNT
BRA.S EMASTX;Exit
END LEA.L I2CR,-(A7);Generate a STOP condition
BCLR.B #5,(A7)+
EMASTX RTE;Return from interrupt
For a master receiver to terminate a data transfer, it must inform the slave transmitter by not
acknowledging the last data byte. This is done by setting I2CR[TXAK] before reading the
next-to-last byte. Before the last byte is read, a STOP signal must be generated, as in the
following example.
MASR MOVE.B RXCNT,D0;Decrease RXCNT
SUBQ.L #1,D0
MOVE.B D0,RXCNT
BEQ.S ENMASR;Last byte to be read
MOVE.B RXCNT,D1;Check second-to-last byte to be read
EXTB.L D1
SUBI.L #1,D1;
BNE.S NXMAR;Not last one or second last
LAMAR BSET.B #3,I2CR;Disable ACK
BRA NXMAR
ENMASR BCLR.B #5,I2CR;Last one, generate STOP signal
NXMAR MOVE.B I2DR,RXBUF;Read data and store RTE
8.6.5 Generation of Repeated START
After the data transfer, if the master still wants the bus, it can signal another START
followed by another slave address without signalling a STOP, as in the following example.
RESTART MOVE.B I2CR,-(A7);Repeat START (RESTART)
BSET.B #2, (A7)
MOVE.B (A7)+, I2CR
MOVE.B CALLING,-(A7);Transmit the calling address, D0=R/W-
MOVE.B CALLING,-(A7);
MOVE.B (A7)+, I2DR