Motorola MC68030 User Manual page 192

Bus Operation
CONTROLLER
LOCK BUS
1) ASSERT READ-MODIFY-WRITE
CYCLE (RMC)
ADDRESS DEVICE
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) SET R/W TO READ
3) DRIVE ADDRESS ON A31-A0
4) DRIVE FUNCTION CODE ON FC2- FC0
5) DRIVE SIZE (SIZ1-SIZ0)
6) CACHE INHIBIT OUT (CIOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE (AS)
8) ASSERT DATA STROBE (DS)
9) ASSERT DATA BUFFER ENABLE (DBEN)
ACQUIRE DATA
1) SAMPLE CACHE INHIBIT IN
2) LATCH DATA
3) NEGATE AS AND DS
4) NEGATE DBEN
5) START DATA MODIFICATION
START OUTPUT TRANSFER
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE ADDRESS ON A31-A0 (IF DIFFERENT)
3) DRIVE SIZE (SIZ1-SIZ0)
4) SET R/W TO WRITE
5) ASSERT AS
6) ASSERT DBEN
7) PLACE DATA ON D31-D0
8) ASSERT DS
TERMINATE OUTPUT TRANSFER
1) NEGATE AS AND DS
2) REMOVE DATA FROM D31-D0
3) NEGATE DBEN
UNLOCK BUS
1) NEGATE RMC
START NEXT CYCLE
Figure 7-29. Asynchronous Read-Modify-Write Cycle Flowchart
7-46
EXTERNAL DRIVE
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON D31-D0
3) ASSERT DATA TRANSFER AND
SIZE ACKNOWLEDGE (DSACKx)
TERMINATE CYCLE
1) REMOVE DATA FROM D31-D0
2) NEGATE DSACKx
ACCEPT DATA
1) DECODE ADDRESS
2) STORE DATA FROM D31-D0
3) ASSERT DSACKx
TERMINATE CYCLE
1) NEGATE DSACKx
MC68030 USER'S MANUAL
A
IF CAS2 INSTRUCTION
AND ONLY ONE OPERAND
READ, THEN GO TO A ;
IF OPERANDS DO NOT
MATCH, THEN GO TO
C ; ELSE GO TO
C
B
B
D
IF CAS2 INSTRUCTION
AND ONLY ONE OPERAND
WRITTEN, THEN GO TO
D ; ELSE GO TO E
E
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