Specifications

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Fig. 1-6 SFR and General Purpose Registers

General-Purpose Registers

General-Purpose registers are used for storing temporary data and results created during operation. For example, if the

program performs a counting (for example, counting products on the assembly line), it is necessary to have a register

which stands for what we in everyday life call “sum”. Since the microcontroller is not creative at all, it is necessary to

specify the address of some general purpose register and assign it a new function. A simple program to increment the

value of this register by 1, after each product passes through a sensor, should be created.

Therefore, the microcontroller can execute that program because it now knows what and where the sum which must be

incremented is. Similarly to this simple example, each program variable must be preassigned some of general-purpose

SFR Registers

Special-Function registers are also RAM memory locations, but unlike general-purpose registers, their purpose is

predetermined during manufacturing process and cannot be changed. Since their bits are physically connected to

particular circuits on the chip (A/D converter, serial communication module, etc.), any change of their contents directly

affects the operation of the microcontroller or some of its circuits. For example, by changing the TRISA register, the

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