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2

Unit Loading/Fan Out

Functional Description

mode of operation, as indicated in the Function Select

Table. An extensive listing of input and output levels is

shown in the Truth Table. The circuit performs the arith-

metic functions for either active HIGH or active LOW oper-

ands, with output levels in the same convention. In the

Subtract operating modes, it is necessary to force a carry

(HIGH for active HIGH operands, LOW for active LOW

The Carry Generate (G) and Carry Propagate (P) outputs

supply input signals to the 74F182 carry lookahead gener-

ator for expansion to longer word length, as shown in Fig-

ure 2. Note that an 74F382 ALU is used for the most

significant package. Typical delays for Figure 2 are given in

Figure 1.

Function Select Table

H

= HIGH Voltage Level

L

= LOW Voltage Level

FIGURE 1. 16-Bit Delay Tabulation

FIGURE 2. 16-Bit Lookahead Carry ALU Expansion

Pin Names

Description

U.L.

HIGH/LOW

A Operand Inputs

1.0/3.0

20

µA/−1.8 mA

B Operand Inputs

1.0/3.0

20

µA/−1.8 mA

Function Select Inputs

1.0/1.0

20

µA/−0.6 mA

Carry Input

1.0/4.0

20

µA/−2.4 mA

G

Carry Generate Output (Active LOW)

50/33.3

−1 mA/20 mA

P

Carry Propagate Output (Active LOW)

50/33.3

−1 mA/20 mA

Function Outputs

50/33.3

−1 mA/20 mA

Select

Operation

LLL

Clear

H

L

L

B Minus A

L

H

L

A Minus B

HH

L

A Plus B

LL

H

A

⊕B

HL

H

A

+ B

LH

H

AB

HHH

Preset

Path Segment

Toward

Output

F

7.2 ns

7.2 ns

6.2 ns

6.2 ns

8.1 ns

—

—

8.0 ns

Total Delay

21.5 ns

21.4 ns