Standard Article


  1. Bruce W. Bomar

Published Online: 13 JUN 2008

DOI: 10.1002/9780470050118.ecse240

Wiley Encyclopedia of Computer Science and Engineering

Wiley Encyclopedia of Computer Science and Engineering

How to Cite

Bomar, B. W. 2008. Microprogramming. Wiley Encyclopedia of Computer Science and Engineering. 1–7.

Author Information

  1. The University of Tennessee Space Institute, Tullahoma, Tennessee

Publication History

  1. Published Online: 13 JUN 2008


The microprogrammed approach to implementing control state machines has been used widely since the early 1960s and has the advantages of structured programming and fixed timing characteristics. With microprogramming, state machine changes require only a change in memory contents, so the rate at which the controller can be clocked does not change no matter how significant the program change. This approach is in contrast to the standard state machine approach with state transitions described in a hardware description language like VHDL or Verilog, where design changes can dramatically impact the logic equations, amount of combinational logic, and clock frequency. This article introduces the microprogramming technique and presents a microprogrammed control unit that has been tailored to implementation in field programable gut arrays. The sequencer presented supports both nested subroutines and nested loops and can operate in both pipelined and non-pipelined modes. Althouse not attractive for a small number of states, the microprogrammed approach has significant advantages for complex controllers with a large number of states.


  • microprogramming;
  • microinstructions;
  • FPGA;
  • pipelining;
  • state;
  • machines;
  • programmable logic devices;
  • circuit;
  • logic circuits