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:

Addition

Subtraction

Shift Operand A One Position

Magnitude Comparison

Plus Twelve Other Arithmetic

Operations

Logic Function Modes:

Exclusive-OR

Comparator

AND, NAND, OR, NOR

Plus Ten Other Logic Operations

description

The LST81 and ‘S181 aro arithmetic logic wits (ALU function generators tht have » complet of 75 equivalent

gates on a manolthic chip. These circuits parform 16 binary arithmetic operations on two 4-bi words 8s shown in

Tables 1 and 2. These operations ar selected by the four function. select nes (50, 51, 52, 53) and include addon,

subtracion, decrement, and suaight transfer. When performing arithmetic manipulations, th internal caries must

be enabled by applying a owovel volage tthe mode control input (M). & ull ary look. ahead scheme s made

availabe in these devices or fest, simultaneous cary generation by means of two cascade. outputs (ons 15 and 17)

for the four bis in the package. When used in conjunction with the SNG4S162 or SN74S182 fu cay look shesd

Gicuits, High-speed arithmetic operations can be performed. The typical addition times shown above lustre the

it ditional time require for odin of longer words whan ful cary look-ahead a employed. The method of

cascading S182 circuits with these ALUS to provide moltavel ful cary look ahasd is utrated under typical

applications data for the 5182.

14 igh speed i not of importance, a ippe-cary input (Ce) and a rpple-carry output (C.) are avallable. However,

he riope-cary delay has iso been minimized 80 tht arthetc man uations for small word angen can bs performed

without extemal circuitry.