DESCRIPTION (continued)

comparison. The A = B output is open-drain so that it

can be wire-AND connected to give a comparison for

more that four bits. The carry output (Cn + 4) can also

be used to supply relative magnitude information.

Again, the ALU should 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 de-

signed to not only incorporate all of the designer’s re-

quirements for arithmetic operations, but also to pro-

vide 16 possible functions of two Boolean variables

without the use of external circuitry. These logic func-

tions are selected by use of the four function-select in-

puts (S0, S1, S2, S3) with the mode-control input (M)

at a high level to disable the internal carry. All inputs

are equipped with protection circuits against static dis-

charge and transient excess voltage.

PIN DESCRIPTION

PIN No

SYMBOL

NAME AND FUNCTION

2, 23, 21, 19

A0 to A3

Word A Inputs

1, 22, 20, 18

B0 to B3

Word B Inputs

6, 5, 4, 3

S0 to S3

Function Select Inputs

7

Cn

Inv. Carry Input

8

M

Mode Control Input

9, 10, 11, 13

F0 to F3

Function Outputs

14

A = B

Comparator Output

15

P

Carry Propagate Output

16

Cn + 4

Inv. Carry Output

17

G

Carry Generate Output

12

GND

Ground (0V)

24

Positive Supply Voltage

INPUT AND OUTPUT EQUIVALENT CIRCUITS

PIN NUMBER

2

1

23

22

21

20

19

18

9

10

11

13

7

16

15

17

ACTIVE LOW DATA (Table 1)

A0

B0

A1

B1

A2

B2

A3

B3

F0

F1

F2

F3

Cn

Cn + 4

P

G

ACTIVE HIGH DATA (Table 1)

A0

B0

A1

B1

A2

B2

A3

B3

F0

F1

F2

F3

Cn

Cn + 4

X

Y

Input Cn

Output Cn + 4

Active LOW Data (Figure 1)

Active HIGH Data (Figure 2)

HH

A

≥ BA ≤ B

HL

A < B

A > B

LH

A > B

A < B

LL

A

≤ BA ≥ B

IEC LOGIC SYMBOLS

ONLY OUTPUT A = B

M74HC181

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