Byte Read Cycle Flowchart - Motorola MC68020 User Manual

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
1) LATCH DATA
2) NEGATE AS AND DS
* 3) NEGATE DBEN
START NEXT CYCLE
*
This step does not apply to the MC68EC020.
** For the MC68EC020, A23–A0.
MOTOROLA
PROCESSOR
ACQUIRE DATA
Figure 5-20. Byte Read Cycle Flowchart
M68020 USER'S MANUAL
EXTERNAL DEVICE
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
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