mc68ec020 Freescale Semiconductor, Inc, mc68ec020 Datasheet - Page 87

• Manufacturer Part Number: mc68ec020
• Description: Microprocessors
• Manufacturer: Freescale Semiconductor, Inc

5-40
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1) ASSERT RMC
1) NEGATE RMC
This step does not apply to the MC68EC020.
For the MC68EC020, A23–A0.
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) SET R/W TO READ
3) DRIVE ADDRESS ON A31–A0
4) DRIVE FUNCTION CODES ON FC2–FC0
5) DRIVE SIZ1, SIZ0
6) ASSERT AS
7) ASSERT DS
8) ASSERT DBEN
1) LATCH DATA
2) NEGATE AS AND DS
3) NEGATE DBEN
4) START DATA MODIFICATION
1) ASSERT ECS/OCS FOR ONE-HALF CLOCK
2) DRIVE ADDRESS ON A31–A0 (IF DIFFERENT)
3) DRIVE SIZ1, SIZ0
4) SET R/W TO WRITE
5) ASSERT AS
6) ASSERT DBEN
7) PLACE DATA ON D31–D0
8) ASSERT DS
1) NEGATE AS AND DS
2) REMOVE DATA FROM D31–D0
3) NEGATE DBEN
TERMINATE OUTPUT TRANSFER
START OUTPUT TRANSFER
START NEXT CYCLE
ADDRESS DEVICE
ACQUIRE DATA
UNLOCK BUS
PROCESSOR
LOCK BUS
Figure 5-29. Read-Modify-Write Cycle Flowchart
M68020 USER’S MANUAL
1) NEGATE DSACK1/DSACK0
1) DECODE ADDRESS
2) PLACE DATA ON D31–D0
3) ASSERT DSACK1/DSACK0
1) REMOVE DATA FROM D31–D0
2) NEGATE DSACK1/DSACK0
1) DECODE ADDRESS
2) STORE DATA FROM D31–D0
3) ASSERT DSACK1/DSACK0
TERMINATE CYCLE
TERMINATE CYCLE
PRESENT DATA
ACCEPT DATA
EXTERNAL DEVICE
AND ONLY ONE OPERAND
AND ONLY ONE OPERAND
READ, THEN GO TO A ;
WRITTEN, THEN GO TO
IF OPERANDS DO NOT
IF CAS2 INSTRUCTION
IF CAS2 INSTRUCTION
MATCH, THEN GO TO
D ; ELSE GO TO E
C ; ELSE GO TO B
A
B
D
E
MOTOROLA
C