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Discuss the basic structure of micro-program control unit.OR Explain micro-programmed control unit.

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By Dipali Umre

A micro-programmed control unit is a design approach for control units in computers where the control signals and sequencing information are stored in a ROM (Read-Only Memory) or RAM (Random Access Memory), which is known as Control Memory (CM). The basic structure of a micro-programmed control unit is illustrated in the provided block diagram (image). Here are the key components and features of a micro-programmed control unit:

  1. Control Memory (CM):
    • The heart of the micro-programmed control unit is the Control Memory. It can be implemented using ROM or RAM.
    • Control signals and sequencing information for various micro-operations are stored in this memory.
  2. Memory Control Word:
    • A memory control word is written for each micro-operation. These control words contain information about the control signals to be generated.
  3. Serial Access Memory:
    • The control memory is accessed serially. This means that control words are read sequentially from the memory, one after the other.
  4. Permanent Storage:
    • Control words are stored permanently in the ROM or RAM. This is because the micro-programmed control unit relies on a fixed set of control signals for various micro-operations.
  5. Output of Control Memory:
    • The output of the control memory provides the necessary control signals required for the execution of micro-operations.
  6. Next Address Generator:
    • The next address generator is responsible for generating the address for the next control word to be read from the control memory.
    • The sequential access of the control memory is often achieved by incrementing the control memory location.
  1. External Inputs:
    • External inputs, which may include status signals from the system or other external sources, can influence the control signals generated by the control unit.
  2. Firmware:
    • The storage of control words in a ROM is often referred to as firmware. Firmware is a type of software that is permanently stored in hardware and is not easily modifiable by the end-user.
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