6 terms

The Instruction Cycle

The instruction cycle for a computer
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Step 1
Fetch: address contained in PC accessed / loaded into MAR, PC incremented. Memory read / loaded into MDR. MDR contents loaded into IR.
Step 2
Decode: IR contents decoded
Step 3
Evaluate Address: contents of base register / PC offset added, supplied via MARMUX to MAR. Sources selected.
Step 4
Operand Fetch: data at that address loaded into MDR
Step 5
Execute: If operations require execution, here be where that done did.
Step 6
Store results: MDR loaded into DR or memory location specified by operation.