Microprogramming in Computer Architecture

Microprogramming in Computer Architecture – Microprogramming is the process of writing microcode for a microprocessor. Microcode is low-level code that defines how a microprocessor should function when it executes machine-language instructions. Typically, one machine language instruction translates into several microcode instructions. On some computers, the microcode is stored in ROM and can not be modified. On some large computers, it is stored in EPROM and therefore can be replaced with newer versions.

Basic Concepts of Microprogramming

• Control word (CW): A word with each bit for one of the control signals. Each step of the instruction execution is represented by a control word with all of the bits corresponding to the control signals needed for the step set to one.
• Microinstruction: Each step in a sequence of steps in the execution of a certain machine instruction is considered a microinstruction, and it is represented by a control word. All of the bits corresponding to the control signals that need to be asserted in this step are set to 1, and all others are set to 0 (horizontal organization).
• Microprogram: Composed of a sequence of microinstructions corresponding to the sequence of steps in the execution of a given machine instruction.
• Microprogramming: The method of generating the control signals by properly setting the individual bits in a control word of a step.
• Microoperations: In computer central processing units, micro-operations are detailed low-level instructions used in some designs to implement complex machine instructions.