Q. Explain about Control Memory Organization?

One of the simplest ways to organize control memory is to organize micro-instructions for different sub cycles of machine instruction in memory. The Figure below demonstrates such an organisation.

Figure: Control Memory Organisation

Let us give an illustration of control memory organization. Let's take a machine instruction: Branch on zero. This instruction causes a branch to a specified main memory address if result of the last ALU operation is zero which means zero flag is set. Pseudocode of micro-program for this instruction would be;

                         Test "zero flag" If SET branch to label ZERO

                         Unconditional branch to label NON-ZERO 

ZERO:  (Microcode that causes replacement of program counter with address offered in instruction)

    Branch to interrupt or fetch cycle.

NON -ZERO:  (Microcode that can set flags if desired indicating branch hasn't taken place).

    Branch to interrupt or fetch cycle. (For Next- Instruction Cycle)