Central Processor Unit (CPU) in Microcontroller - Microcontroller basics

As its name suggests, this is a unit which monitors and controls all processes inside the microcontroller. It consists of several smaller subunits, of which the most important are:

Instruction Decoder

It is a part of the electronics which recognizes program instructions and runs other circuits on the basis of that. The “instruction set” which is different for each microcontroller family expresses the abilities of this circuit.

Arithmetical Logical Unit (ALU)

It performs all mathematical and logical operations upon data.


It is a SFR closely related to the operation of the ALU. It is a kind of working desk used for storing all data upon which some operation should be performed (addition, shift/move etc.). It also stores the results ready for use in further processing. One of the SFRs, called a Status Register (PSW), is closely related to the accumulator. It shows at any given moment the “status” of a number stored in the accumulator (number is greater or less than zero etc.).

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