74F182 Просмотр технического описания (PDF) - Fairchild Semiconductor

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74F182

Carry Lookahead Generator

Fairchild Semiconductor 

Unit Loading/Fan Out

Pin Names

Description

Cn

G0, G2

G1

G3

P0, P1

P2

P3

Cn+x − Cn+z

G

P

Carry Input

Carry Generate Inputs (Active LOW)

Carry Generate Input (Active LOW)

Carry Generate Input (Active LOW)

Carry Propagate Inputs (Active LOW)

Carry Propagate Input (Active LOW)

Carry Propagate Input (Active LOW)

Carry Outputs

Carry Generate Output (Active LOW)

Carry Propagate Output (Active LOW)

U.L.

HIGH/LOW

1.0/2.0

1.0/14.0

1.0/16.0

1.0/8.0

1.0/8.0

1.0/6.0

1.0/4.0

50/33.3

50/33.3

50/33.3

Input IIH/IIL

Output IOH/IOL

20 µA/−1.2 mA

20 µA/−8.4 mA

20 µA/−9.6 mA

20 µA/−4.8 mA

20 µA/−4.8 mA

20 µA/−3.6 mA

20 µA/−2.4 mA

−1 mA/20 mA

−1 mA/20 mA

−1 mA/20 mA

Functional Description

The 74F182 carry lookahead generator accepts up to four

pairs of Active LOW Carry Propagate (P0–P3) and Carry

Generate (G0–G3) signals and an Active HIGH Carry input

(Cn) and provides anticipated Active HIGH carries (Cn + x,

Cn+y, Cn+z) across four groups of binary adders. The

74F182 also has Active LOW Carry Propagate (P) and

Carry Generate (G) outputs which may be used for further

levels of lookahead. The logic equations provided at the

outputs are:

Cn+x = G0 + P0 Cn

Cn+y = G1 + P1 G0 + P1 P0 Cn

Cn+z = G2 + P2 G1 + P2 P1 G0 + P2 P1 P0 Cn

G = G3 + P3 G2 + P3 P2 G1 + P3 P2 P1 G0

P = P2 P2 P1 P0

Also, the 74F182 can be used with binary ALUs in an

active LOW or active HIGH input operand mode. The con-

nections (Figure 1) to and from the ALU to the carry looka-

head generator are identical in both cases. Carries are

rippled between lookahead blocks. The critical speed path

follows the circled numbers. There are several possible

arrangements for the carry interconnects, but all achieve

about the same speed. A 28-bit ALU is formed by dropping

the last 74F181 or 74F381.

*ALUs may be either 74F181 or 74F381

FIGURE 1. 32-Bit ALU with Rippled Carry between 16-Bit Lookahead ALUs

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