Freescale Semiconductor, Inc.
BYTE OPERAND
OP0
0
7
DATA BUS
CYCLE 1
D15
OP0
D8 D7
(OP0)
D0
SIZ1
0
SIZ0
1
A0
X
DSACK1 DSACK0
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.
3.2.3.2 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.
BYTE OPERAND
OP0
OP0
0
7
DATA BUS
CYCLE 1
D15
D8 D7
D0
SIZ1
SIZ0
A0
DSACK1 DSACK0
0
1
0
0
X
(OP0)
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- 8
MC68340 USER’S MANUAL
MOTOROLA
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