Motorola MCF5282 ユーザーズマニュアル

24-12

MOTOROLA

 

the interrupt routine. I2SR[ICF] is cleared either by reading from I2DR in receive mode or
by writing to I2DR in transmit mode.

Software can service the I

2

C I/O in the main program by monitoring IIF if the interrupt

function is disabled. Polling should monitor IIF rather than ICF because that operation is
different when arbitration is lost.

When an interrupt occurs at the end of the address cycle, the master is always in transmit
mode; that is, the address is sent. If master receive mode is required I2CR[MTX] should be
toggled.

During slave-mode address cycles (I2SR[IAAS] = 1), I2SR[SRW] is read to determine the
direction of the next transfer. MTX is programmed accordingly. For slave-mode data cycles
(IAAS = 0), SRW is invalid. MTX should be read to determine the current transfer
direction.

The following is an example of a software response by a master transmitter in the interrupt
routine (see Figure 24-10).

I2SR

LEA.L I2SR,-(A7)

;Load effective address

BCLR.B #1,(A7)+

;Clear the IIF flag

MOVE.B I2CR,-(A7)

;Push the address on stack,

BTST.B #5,(A7)+

;check the MSTA flag

BEQ.S SLAVE

;Branch if slave mode

MOVE.B I2CR,-(A7)

;Push the address on stack

BTST.B #4,(A7)+

;check the mode flag

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

TRANSMIT MOVE.B DATABUF,-(A7)

;Stack data byte

MOVE.B (A7)+, I2DR

;Transmit next byte of data

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