MC68020 Motorola, MC68020 Datasheet - Page 164

• Manufacturer Part Number: MC68020
• Description: (MC68020 / MC68EC020) MICROPROCESSORS USERS MANUAL
• Manufacturer: Motorola

After evaluating the condition, the coprocessor returns a true/false indicator to the main
processor by placing a null primitive (refer to 7.4.4 Null Primitive) in the response CIR.
The main processor completes the coprocessor instruction execution when it receives the
condition indicator from the coprocessor.
MOTOROLA
M1
OPERATION WORD
M2
CO
M3
FROM RESPONSE CIR
1) PERFORM SERVICE REQUESTED BY RESPONSE
PRIMITIVE
2) IF (COPROCESSOR RESPONSE PRIMITIVE
INDICATES "COME AGAIN") GO TO M3
(SEE NOTE)
M4
ON THE TRUE/FALSE CONDITION INDICATOR
RETURNED IN THE RESPONSE CIR
NOTE: All coprocessor response primitives, except the Null primitive, that allow the "Come Again" primitive attribute
NDITION CIR
WRITE COPROCESSOR CONDITION SELECTOR TO
RECOGNIZE COPROCESSOR INSTRUCTION F-LINE
READ COPROCESSOR RESPONSE PRIMITIVE CODE
COMPLETE EXECUTION OF INSTRUCTION BASED
must indicate "Come Again" when used during the execution of a conditional category instruction. If a "Come
Again" attribute is not indicated in one of these primitives, the main processor will initiate protocol violation
exception processing (see 7.5.2.1 Protocol Violations).
MAIN PROCESSOR
Figure 7-8. Coprocessor Interface Protocol
for Conditional Category Instructions
M68020 USER’S MANUAL
C1
COMMAND EXECUTION
C2
DO STEPS 1) AND 2) BELOW
1) REQUEST SERVICE BY PLACING APPROPRIATE
2) RECEIVE SERVICE FROM MAIN PROCESSOR
C3
C4
CONDITION INDICATOR IN RESPONSE CIR
DECODE COMMAND WORD AND INITIATE
WHILE (MAIN PROCESSOR SERVICE IS REQUIRED)
COMPLETE CONDITION EVALUATION
REFLECT "NO COME AGAIN" STATUS WITH TRUE/FALSE
RESPONSE PRIMITIVE CODE IN RESPONSE CIR
COPROCESSOR
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