What is a microprogram



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A microprogram is a sequence of instructions (microinstructions) that can be executed by the hardware (processor).

Since the transistors of the processor only understand ON (current flows) or OFF (current interrupted), a microinstruction consists of a line of ones and zeros (binary digits = bits).

Depending on where there is a zero or a one in the line (according to the microinstruction format), certain switches are set to ON and others to OFF.

A series of such lines (microprogram) changes the state of the hardware at regular intervals (cycle).

For example, certain cables (e.g. address or data bus) are switched on or command counters (pointer that points to the address of the next command to be executed) are changed, etc.

A micro-command is executed in each cycle, i.e. 100,000 micro-commands are processed per second at 100 MHz (today there are already computers with more than one gigahertz).

3 to 6 micro-commands form a machine command (read, decode, process, write)

1 to 5 machine commands are put together to form a machine command cycle (get address for data and command, read data, decode data and command, apply command to data, save data to memory address).

Many successive machine instruction cycles form a program.

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