The central function of a computer is to perform operations on data. This is done with an Arithmetic/Logic Unit or ALU.

This article presents an ALU that may be used to build a computer core around or used for other calculation needs.

This shows the testing setup for the ALU:

ALU setup

The layout of the ALU is modular:

ALU bitwise

Each 'column' performs one operation and all operations are performed at the same time, in parallel. You can see that some functions are done by the logic gates while others use programmed memory banks. Some functions operated on both inputs, such as the 'AND' operation. Others, such as 'NOT ' only operate on one input. The Input A is the dominant one and is always used for single operand functions.

Only one result is enabled to the output bus, at any time. The vertical banks function as the multiplexer for the outputs. The opcode signal is the control to these banks and selects which output is enabled. This parallel arrangement allows for very fast operation.

Details on the layout:

ALU basic

You can see the two input busses, the output bus and the opcode signal. The source for these are not discussed in this article. The first picture shows a test setup where the input values and opcode are set by the user.

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