MC68340 datasheet(57/441 Pages) FREESCALE

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3- 8

MC68340 USER’S MANUAL

MOTOROLA

DSACK0

DSACK1

SIZ0

SIZ1

D15

(OP0)

OP0

BYTE OPERAND

DATA BUS

CYCLE 1

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.

3.2.3.2 BYTE 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.

DSACK0

DSACK1

SIZ0

SIZ1

0100

D15

(OP0)

OP0

BYTE OPERAND

DATA BUS

CYCLE 1

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.

Freescale Semiconductor, Inc.

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