© 2000 Fairchild Semiconductor Corporation

DS006474

www.fairchildsemi.com

August 1986

Revised March 2000

DM74S182

Look-Ahead Carry Generator

General Description

These circuits are high-speed, look-ahead carry genera-

tors, capable of anticipating a carry across four binary

adders or groups of adders. They are cascadable to per-

form full look-ahead across n-bit adders. Carry, generate-

carry, and propagate-carry functions are provided as

shown in the pin designation table.

When used in conjunction with the 181 arithmetic logic unit,

these generators provide high-speed carry look-ahead

capability for any word length. Each DM74S182 generates

the look-ahead (anticipated carry) across a group of four

ALU’s and, in addition, other carry look-ahead circuits may

be employed to anticipate carry across sections of four

look-ahead packages up to n-bits. The method of cascad-

ing circuits to perform multi-level look-ahead is illustrated

under typical application data.

Carry input and output of the ALU’s are in their true form,

and the carry propagate (P) and carry generate (G) are in

negated form; therefore, the carry functions (inputs, out-

puts, generate, and propagate) of the look-ahead genera-

tors are implemented in the compatible forms for direct

connection to the ALU. Reinterpretations of carry functions,

as explained on the 181 data sheet are also applicable to

and compatible with the look-ahead generator. Positive

logic equations for the DM74S182 are:

G

= G3 (P3 + G2) (P3 + P2 + G1)

(P3

+ P2 + P1 + G0)

P

= P3 P2 P1 P0

Features

s Typical propagation delay time 7 ns

s Typical power dissipation 260 mW

Ordering Code:

Connection Diagram

Pin Designations

Order Number

Package Number

Package Description

DM74S182N

N16E

16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide

Designation

Pin Nos.

Function

G0, G1, G2, G3

3, 1, 14, 5

Active LOW

Carry Generate Inputs

P0, P1, P2, P3

4, 2, 15, 6

Active LOW

Carry Propagate Inputs

13

Carry Input

12, 11, 9

Carry Outputs

G

10

Active LOW

Carry Generate Output

P

7

Active LOW

Carry Propagate Output

16

Supply Voltage

GND

8

Ground