Motorola MC68340 manual OP0 Data BUS

Freescale Semiconductor, Inc...

Freescale Semiconductor, Inc.

BYTE OPERAND	OP0
	7	0
DATA BUS	D15	D8 D7		D0	SIZ1	SIZ0	A0	DSACK1	DSACK0
CYCLE 1	OP0		(OP0)		0	1	X	1	0

For a read operation, the slave responds by placing data on bits 15–8 of the data bus, asserting DSACK0 and negating DSACK1 to indicate an 8-bit port. The MC68340 then reads the operand byte from bits 15–8 and ignores bits 7–0.

For a write operation, the MC68340 drives the single-byte operand on both bytes of the data bus because it does not know the port size until the DSACK≈ signals are read. The slave device reads the byte operand from bits 15–8 and places the operand in the specified location. The slave then asserts DSACK0 to terminate the bus cycle.

3.2.3.2BYTE OPERAND TO 16-BIT PORT, EVEN (A0 = 0). The MC68340 drives the address bus with the desired address and the SIZx pins to indicate a single-byte operand.

BYTE OPERAND		OP0
	7		0
DATA BUS	D15		D8	D7	D0	SIZ1	SIZ0	A0	DSACK1	DSACK0
CYCLE 1		OP0		(OP0)		0	1	0	0	X

For a read operation, the slave responds by placing data on bits 15–8 of the data bus and asserting DSACK1 to indicate a 16-bit port. The MC68340 then reads the operand byte from bits 15–8 and ignores bits 7–0.

For a write operation, the MC68340 drives the single-byte operand on both bytes of the data bus because it does not know the port size until the DSACK≈ signals are read. The slave device reads the operand from bits 15–8 of the data bus and uses the address to place the operand in the specified location. The slave then asserts DSACK1 to terminate the bus cycle.

3- 8MC68340 USER’S MANUALMOTOROLA

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