What is the principle of full adder?

Full adder principle: 1. A one-bit full adder can handle low-bit carry and output the local addition carry; 2. Multiple one-bit full adders can be cascaded to obtain a multi-bit full adder, which is commonly used Binary four-bit full adder 74LS283.

#The operating environment of this article: Windows 7 system, Dell G3 computer.

Principle of full adder:

The English name of the full adder is full-adder, which is a combination of using gate circuits to add two binary numbers and find the sum. circuit, called a one-bit full adder. A one-bit full adder can handle the low-bit carry and output the local addition carry. A multi-bit full adder can be obtained by cascading multiple one-bit full adders. The commonly used binary four-bit full adder 74LS283.

The logical expression of a one-bit full adder (FA) is:

S＝A⊕B⊕Cin; Cout＝AB＋BCin＋ACin, where A and B are the numbers to be added, Cin is the carry input; S is the sum, and Co is the carry output; if you want to implement multi-bit addition, you can cascade it, that is, use it in series.

For example, 32-bit 32-bit, 32 full adders are needed; this cascade means that the serial structure is slow. If you want to add quickly in parallel, you can use carry-lookahead addition.

If the input of the full adder is replaced by the combined functions Xi and Y of A and B (controlled by S0...S3), and then X, Y and the carry number are fully added through the full adder, it is ALU logical structure. That is, X = f (A, B); Y = f (A, B). Different control parameters can obtain different combination functions, thus enabling a variety of arithmetic operations and logical operations.

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