Arithmetic Logic Unit

ALU

•      a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers.

•      MIPS word is 32-bits wide, so 32-bit-wide ALU.

Arithmetic Logic Unit schematic symbol

1-Bit ALU

The half adder adds two single binary digits A and B.  It has two outputs, sum (S) and carry (C).

The carry signal represents an overflow into the next digit of a multi-digit addition.

The value of the sum is 2C + S.

The simplest half-adder design, pictured on the right,

incorporates an XOR gate for S and an AND gate for C.

With the addition of an OR gate to combine their carry

outputs, two half adders can be combined to make a full adder. 

A full adder adds binary numbers and accounts for values carried in as well as out.

A one-bit full adder adds three one-bit numbers, often written as A, B, and Cin; A and B are

the operands, and Cin is a bit carried in from the next less significant stage. 

The circuit produces a two-bit output sum typically represented by the signals Cout and S .

The one-bit full adder's truth table is:

Written by

Name: Su’aidah Binti Mokhtar

No. Matrik: B031210193