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In horizontal micro-programming the control word is of the following format:

Flag bits Control Signal Bits Next Control Word Address

I know that the Control Signal bits denote which micro-operation to execute. My question is does 1 bit of control signal denote one micro-operation entirely ? Or some combination of set bits in the control word denote one micro-operation?

For example:

  Consider the micro-operation: MDR <-- PC .

  Now, suppose the control signal is of 8 bits  _ _ _ _   _ _ _ _ .

  Scenario 1:

           The 0th bit in the control signal word gives WRITE signal to the PC and the 1st bit in the  control signal word gives READ signal to MDR. So that when both of them are ON, the MDR would read the contents of PC. i.e. the micro-operation MDR <-- PC is given by the control signal 00000011. Here one control signal bit is denoting only one signal. And multiple control signal bits need to be ON in order to denote 1 micro-operation.

  Scenario 2:

           The 0th bit in the control signal word gives both the WRITE signal to the PC and also READ signal to MDR. So that when only the 0th bit is ON, the MDR would read the contents of PC. i.e. the micro-operation MDR <-- PC is given by the control signal 00000001. Here 1 control signal bit is denoting 1 micro-operation entirely.

I previously thought that Scenario 1 was always done. But this question https://gateoverflow.in/2254/gate1997_5-3 changed my view. Here 1 control signal bit is used to denote 1 micro-operation.

Can someone please verify that Scenario 2 is the correct one i.e. 1 control signal bit in horizontal microprogramming denotes 1 micro-operation entirely?

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