Industrial Training




Control Unit



A CU takes its input from the instruction and status registers. Its rules of operation, or microprogram, are encoded in a programmable logic array (PLA), random logic or read-only memory (ROM).



CU functions are as follows:

  • Controls sequential instruction execution
  • Interprets instructions
  • Guides data flow through different computer areas
  • Regulates and controls processor timing
  • Sends and receives control signals from other computer devices
  • Handles multiple tasks, such as fetching, decoding, execution handling and storing results


CUs are designed in two ways:

  • Hardwired control: Design is based on a fixed architecture. The CU is made up of flip-flops, logic gates, digital circuits and encoder and decoder circuits that are wired in a specific and fixed way. When instruction set changes are required, wiring and circuit changes must be made. This is preferred in a reduced instruction set computing (RISC) architecture, which only has a small number of instructions.
  • Microprogram control: Microprograms are stored in a special control memory and are based on flowcharts. They are replaceable and ideal because of their simplicity


Control Unit

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