Motorola MC68020 - Word Operand Write to Byte Port Example

5- 12 M68020 USER’S MANUAL MOTOROLA
Figure 5-7 shows a word write to an 8-bit bus port. Like the preceding example, this
example requires two bus cycles. Each bus cycle transfers a single byte. SIZ1 and SIZ0
for the first cycle specify two bytes; for the second cycle, one byte. Figure 5-8 shows the
associated bus transfer signal timing.
OP2
OP3
15
0
WORD OPERAND
D31
DATA BUS
D24
BYTE MEMORY
OP2
OP3
MC68020/EC020
SIZ1
SIZ0
A1
A0
1 0 0 0
0
1 0 1
MEMORY CONTROL
DSACK1
DSACK0
H
L
H
L
Figure 5-7. Word Operand Write to Byte Port Example