Motorola MC68030 User Manual page 206

PROCESSOR EXTERNAL OEVICE
LOCK BUS
1) ASSERT REAO-MODlFY-WRITE CYCLE (RMC)
+
AOORESS DEVICE
1) ASSERT ECS/OSC FOR ONE-HALF CLOCK
2) SET R/WTO READ
3) ORIVE ADDRESS ON AO-A31
4) DRIVE FUNCTION CODE ON FCO-FC2
5) DRIVE SIZE (SIZO-SIZ1)
6) CACHE INHIBIT OUT (ClOUT) BECOMES VALID
7) ASSERT ADDRESS STROBE
(AS)
8) ASSERT DATA STROBE
(OS)
9) ASSERT DATA BUFFER ENABLE (OBEN)
r-------+
PRESENT DATA
1) DECODE ADDRESS
2) PLACE DATA ON 00-031
3) ASSERT DATA TRANSFER
ACQUIRE DATA
..-
AND SIZE ACKNOWLEDGE (DSACKx)
0
1) SAMPLE CACHE INHIBIT IN (CIIN)
2) LATCH DATA
IF CAS2 INSTRUCTION AND
3) NEGATE
AS
AND
OS
ONLY ONE OPERAND READ.
4) NEGATE DBEN THEN GO TO
0:
IF
5) START DATA MODIFICATION
----.
TERMINATE CYCLE
OPERANDS DO NOT MATCH.
THEN GO TO
@:
ElSE
1) REMOVE DATA FROM 00-031
GOTO®
START OUTPUT TRANSFER
2) NEGATE DSACKx
-..
®
©
I--
1) ASSERT m/OCS FOR ONE-HALF CLOCK
2) DRIVE ADDRESS ON AO-A31 (IF DIFFERENT)
3) DRIVE SIZE (SIZO-SIZI)
+
4) SET R/W TO WRITE
5) ClOUT BECOMES VALID
6) ASSERT
AS
7) ASSERT DBEN
8) PLACE DATA ON 00-031
9) ASSERT
OS
----.
ACCEPT DATA
1) DECODE ADDRESS
®
2) STORE DATA FROM 00-031
TERMINATE OUTPUT TRANSFER
..-
3) ASSERT DSACKx
IF CAS2 INSTRUCTION AND
1) NEGATE
AS
ANO
OS
ONLY ONE OPERAND
2) REMOVE OATA FROM 00-031
WRITIEN. THEN GO TO
@:
3) NEGATE DBEN
,----..
TERMINATE CYCLE
ElSE GDTO
CD
I) NEGATE DSACKx f-----+
CD
UNLOCK BUS
1) NEGATE RMC
t
+
START NEXT CYCLE
Figure 7-29. Asynchronous Read-Modify-Write Cycle Flowchart
7-44
MC68030 USER'S MANUAL MOTOROLA