Motorola MC68020 - Byte Read Cycle Flowchart

MOTOROLA M68020 USER’S MANUAL 5- 27
ACQUIRE DATA
1) LATCH DATA
2
) NEGATE AS AND D
S
3
) NEGATE DBEN
START NEXT CYCLE
PRESENT DATA
1) DECODE ADDRESS
2
) PLACE DATA ON D31–D24 OR
D23–D16 OR
D15–D8 OR
D7–D0
(BASED ON A1, A0, AND BUS WIDTH
)
3
) ASSERT DSACK1/DSACK0
TERMINATE CYCLE
1) REMOVE DATA FROM D31–D0
2
) NEGATE DSACK1/DSACK0
EXTERNAL DEVICE
PROCESSOR
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 SIZ1, SIZ0 (FOUR BYTES)
6
) ASSERT AS
7
) ASSERT DS
8
) ASSERT DBEN
*
*
This step does not apply to the MC68EC020.
For the MC68EC020, A23–A0.
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*
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Figure 5-20. Byte Read Cycle Flowchart