
MOTOROLA
M68020 USER’S MANUAL
5- 27
ACQUIRE DATA
1) LATCH DATA
2) NEGATE AS AND DS
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
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Freescale Semiconductor, Inc.
For More Information On This Product,
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