6.1.2 Explain the role of the above components in theexecution of single instructions in the machine instruction cycle.
(No teaching notes for this one.)
JSR Notes:
So here you have to put together the machine instruction cycle you learned in 3.2.4 with these registers. Where do they fit in. Again, take a good look at the additional information for 6.1 that is posted here, but here's putting each one individually into its own context.
Let's start with a review of the instruction cycle:
Fetch
Decode (and if what is decoded is an address, go fetch whatever is there)
Execute
Store
Now we'll put in the registers, each in isolation: accumulator, instruction, and program counter
Accumulator Register first:
Fetch
Decode
Execute - Most often, during this stage, execution means taking what's in the accumulator and acting on it with the new instruction and its operand.
Store - Most often storing of the result of one instruction means storing of the result in the accumulator (except for the last stage of a process, in which case the stored result is saved to RAM memory.
Instruction Register:
Fetch - This is what is fetched; the instruction (with its opcode instruction and its data [operand]) is requested via the address bus, and brought in for execution.
Decode - It is the instruction in the instruction register which is decoded.
Execute - It is the decoded instruction which is executed.
Store
Program Counter Register:
Fetch - The instruction that is located at the address which is held in the program counter is the instruction that is fetched.
Decode -
Execute -
Store -