Data Bus Requirements For Read Cycles - Motorola MC68020 User Manual

Table 5-4 lists the bytes required on the data bus for read cycles. The entries shown as
OP3, OP2, OP1, and OP0 are portions of the requested operand that are read or written
during that bus cycle and are defined by SIZ1, SIZ0, A1, and A0 for the bus cycle.
Table 5-4. Data Bus Requirements for Read Cycles
Transfer
Size
Size
SIZ1 SIZ0
Byte 0 1
0 1
0 1
0 1
Word 1
1
1
1
3 Bytes 1 1
1 1
1 1
1 1
Long Word 0
0
0
0
5-8
Address
A1 A0 D31–D24
0 0 OP3
0 1
1 0
1 1
0 0 0 OP2
0 0 1
0 1 0
0 1 1
0 0 OP1
0 1
1 0
1 1
0 0 0 OP0
0 0 1
0 1 0
0 1 1
M68020 USER'S MANUAL
Long-Word Port
External Data Bytes
Required
D23–D16 D15–D8 D7–D0
OP3
OP3
OP3
OP3
OP2 OP3
OP2 OP3
OP2
OP2 OP3
OP1 OP2 OP3
OP1 OP2
OP1
OP3
OP1 OP2
OP0 OP1 OP2
OP0 OP1
OP0
Byte Port
Word Port
External
External Data Bytes
Data Bytes
Required
Required
D31–D24 D23–D16 D31–D24
OP3 OP3
OP3 OP3
OP3 OP3
OP3 OP3
OP2 OP3 OP2
OP2 OP2
OP2 OP3 OP2
OP2 OP2
OP1 OP2 OP1
OP1 OP1
OP1 OP2 OP1
OP1 OP1
OP0 OP1 OP0
OP0 OP0
OP0 OP1 OP0
OP0 OP0
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