MC68020 Motorola, MC68020 Datasheet - Page 65

• Manufacturer Part Number: MC68020
• Description: (MC68020 / MC68EC020) MICROPROCESSORS USERS MANUAL
• Manufacturer: Motorola

Figures 5-15 and 5-16 show an example of a long-word transfer (write) to an odd address
in long-word-organized memory. In this example, a long-word access is attempted
beginning at the least significant byte of a long-word-organized memory. Only one byte
can be transferred in the first bus cycle. The second bus cycle then consists of a three-
byte access to a long-word boundary. Since the memory is long word organized, no
further bus cycles are necessary. Figure 5-17 shows the equivalent operation for a data
read cycle.
5-18
31
D31
OP0
Figure 5-14. Misaligned Word Operand Read from Word Bus Example
MSB
OP1
XXX
15
D31
WORD OPERAND (REGISTER)
OP2
Figure 5-15. Misaligned Long-Word Operand Write
MSB
OP3
XXX
WORD MEMORY
OP1
UMB
XXX
OP2
LONG-WORD OPERAND
LONG-WORD MEMORY
DATA BUS
DATA BUS
to Long-Word Port Example
OP2
LSB
XXX
OP3
M68020 USER’S MANUAL
LMB
XXX
OP3
OP2
D16
0
SIZ1 SIZ0 A2
1
0
OP0
LSB
XXX
MC68020/EC020
OP3
0
1
0
0
D0
0
A1
0
1
SIZ1 SIZ0 A2
0
1
A0
1
0
MC68020/EC020
0
1
0
1
MEMORY CONTROL
DSACK1
L
L
A1
1
0
A0
1
0
DSACK0
H
H
MEMORY CONTROL
DSACK1
L
L
MOTOROLA
DSACK0
L
L