SN54S181 Arithmetic Logic Units/Function Generators | TI.com

# Arithmetic Logic Units/Function Generators

Datasheet

• Description
• Features
• Diagram
• Parametrics
• Applications for you

## Description

If high speed is not of importance, a ripple-carry input (Cn) and a ripple-carry output (Cn+4) are available. However, the ripple-carry delay has also been minimized so that arithmetic manipulations for small word lengths can be performed without external circuitry.

The 'LS181 and 'S181 will accommodate active-high data if the pin designations are interpreted as follows:

Subtraction is accomplished by 1's complement addition where the 1's complement of the subtrahend is generated internally.The resultant output is A – B – 1, which requires an end-around or forced carry to provide A – B.

The 'LS181 or 'S181 can also be utilized as a comparator. The A = B output is internally decoded from the function outputs (F0, F1, F2, F3) so that when two words of equal magnitude are applied at the A and B inputs, it will assume a high level to indicate equality (A = B). The ALU must be in the subtract mode with Cn = H when performing this comparison. The A = B output is open-collector so that it can be wire-AND connected to give a comparison for more than four bits. The carry output (Cn+4) can also be used to supply relative magnitude information. Again, the ALU must be placed in the subtract mode by placing the function select inputs S3, S2, S1, S0 at L, H, H, L, respectively.

These circuits have been designed to not only incorporate all of the designer's requirements for arithmetic operations, but also to provide 16 possible functions of two Boolean variables without the use of external circuitry. These logic functions are selected by use of the four function-select inputs (S0, S1, S2, S3) with the mode-control input (M) at a high level to disable the internal carry. The 16 logic functions are detailed in Tables 1 and 2 and include exclusive-OR, NAND, AND, NOR, and OR functions.

Series 54, 54LS, and 54S devices are characterized for operation over the full military temperature range of -55°C to 125°C; Series 74LS and 74S devices are characterized for operation from 0°C to 70°C.

## Features

• Full Look-Ahead for High-Speed Operations on Long Words
• Input Clamping Diodes Minimize Transmission-Line Effects
• Darlington Outputs Reduce Turn-Off Time
• Arithmetic Operating Modes: