Fairchild Semiconductor 74F181SPC, 74F181SCX, 74F181SC, 74F181PC Datasheet

© 1999 Fairchild Semiconductor Corporation DS009491 www.fairchildsemi.com

April 1988
Revised July 1999

74F181 4-Bit Arithmetic Logic Unit

74F181
4-Bit Arithmetic Logic Unit

General Description

The 74F181 is a 4-bit Arithmetic logic Unit (ALU) which can
perform all the po ssible 16 logic operations on two vari­ables and a variety of arithmetic operations. It is 40% faster
than the Schottky ALU and only consu mes 30% as much
power.

Features

■ Full lookahead for high-speed arithmetic operation on
long words

Ordering Code:

Devices also availab le in Tape and Reel. Specify by appending th e s uffix let t er “X” to the ordering code.

Logic Symbols

Active-HIGH Operands

Active-LOW Operands

IEEE/IEC

Connection Diagram

Order Number Package Number Package Description

74F181SC M24B 24-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-013, 0.300 Wide
74F181PC N24A 24-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-010, 0.600 Wide
74F181SPC N24C 24-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-100, 0.300 Wide

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74F181

Unit Loading/Fan Out

Note 1: OC-Open C ollector

Functional Description

The 74F181 is a 4-bit high-speed parallel Arithmetic Logic
Unit (ALU). Controlled by the four Function Select inputs
(S

0–S3

) and the Mode Control input (M), it can perform all

the 16 possible log ic operations or 16 different arithmetic
operations on Active HIGH or Active LOW operands. The
Function Table lists these operations.

When the Mode Control input (M) is HIGH, all internal car­ries are inhibited and the device p erforms l ogic oper ations
on the individual bits as listed. When the Mode Control
input is LOW, the carries are enabled and the dev ice per­forms arithmetic operations on the two 4-bit words. The
device incorporates full internal carry l ookahead and pro­vides for either ripple carry between devices using the
C

n + 4

output, or for carry lookahead between packages

using the signals P

(Carry Propagate) and G (Carry Gener-

ate). In the Add mode, P

indicates that F is 15 or more,

while G

indicates that F is 16 or more. In the Subtract mode

P

indicates that F is zero or less, while G indicates that F is

less than zero. P

and G are not affected by carry in. When
speed requiremen ts are not stringent , the 74F181 can be
used in a simple Ripple Carry mode by connecting the
Carry output (C

n

+4) signal to the Carry input (Cn) of the
next unit. For h igh speed operation t he device is used in

conjunction with a carry lookahead circuit. One carry looka­head package is requ ired for each group of four 74F181

devices. Carry lookahead can be provided at various levels
and offers high speed capability over extremely long wo rd
lengths.

The A = B output from the device goes HIGH w hen all four
F

outputs are HIGH and can be used to indicate logic
equivalence over four bits when the u nit is in t he Subtract
mode. The A = B output is open collector and can be wired
AND with other A = B outputs to give a comparison for
more than four bits. The A = B signal can also be used with
the C

n+4

signal to indicate A > B and A < B.

The Function Table lists the arithmetic ope rations that are
performed without a carry in. An incoming carry adds a one
to each operation . Thus, select code LHHL gene rates A
minus B minus 1 (2s complem ent no tation) witho ut a ca rry
in and generates A minus B when a carry is applied.
Because subtraction is actual ly performed by co mplemen­tary addition (1s complement), a carry out means borrow

;
thus a carry is gener ated when there is no underflow a nd
no carry is generated when there is underflow. As indi­cated, this device can be used with either active LOW
inputs producing active LOW outputs or with active HIGH
inputs producing active HIGH outp uts. For either case the
table lists the operatio ns that are performed to the oper­ands labeled inside the logic symbol.

Pin Names Description

U.L.

Input I

IH/IIL

HIGH/LOW

Output I

OH/IOL

A0–A

3

A Operand Inputs (Active LOW) 1.0/3.0 20 µA/−1.8 mA

B

0–B3

B Operand Inputs (Active LOW) 1.0/3.0 20 µA/−1.8 mA

S

0–S3

Function Select Inputs 1.0/4.0 20 µA/−2.4 mA
M Mode Control Input 1.0/1.0 20 µA/−0.6 mA
C

n

Carry Input 1.0/5.0 20 µA/−3.0 mA
F

0–F3

Function Outputs (Active LOW) 50/33.3 −1 mA/20 mA
A = B Comparator Output OC (Note 1)/33.3 (Note 1)/20 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
C

n + 4

Carry Output 50/33.3 −1 mA/20 mA

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74F181

Operation Table

Logic Arithmetic Arithmetic

S

0S1S2S3

(M=H) (M=L, C0=Inactive) (M=L, C0=Active)

a. All Input Data Inverted

LLLL A

A minus 1 A

HLLL A

• B A • B minus 1 A • B

LHLL A

+ BA • B minus 1 A • B
H H L L Logic “1” minus 1 (2s comp.) Zero
LLHL A

+ B A plus (A + B) A plus (A + B) plus 1

HLHL B

A • B plus (A + B) A • B plus (A + B) plus 1

LHHLA

⊕ B A minus B minus 1 A minus B

HHHL A + B

A + B A + B plus 1

LLLHA

• B A plus (A + B) A plus (A + B plus 1
HLLH A⊕B A plus B A plus B plus 1
LHLH B A • B

plus (A + B) A • B plus (A + B) plus 1
HHLH A + BA + BA + B plus 1
L L H H Logic “0” A plus A (2 × A) A plus A (2 × A) plus 1
HLHH A • B

A plus A • B A plus A • B plus 1

L H H H A • B A plus A • B

A plus A • B plus 1

HHHH A A A plus 1

b. All Input Data True

LLLL A

A A plus 1

HLLLA

+ B A + BA + B plus 1

LHLL A

• B A + B A + B plus 1
H H L L Logic “0” minus 1 (2s comp.) Zero
LLHL A

• B A plus (A • B)A plus A • B plus 1
HLHL B

A • B plus (A + B) A • B plus (A + B) plus 1
LHHLA ⊕ B A minus B minus 1 A minus B
HHHL A • B

A • B minus 1 A • B
LLLHA + B A plus A • B A plus A • B plus 1
HLLH A

⊕B A plus B A plus B plus 1

LHLH B A • B plus (A + B

) A • B plus (A + B) plus 1
H H L H A • B A • B minus 1 A • B
L L H H Logic “1” A plus A (2 × A) A plus A (2 × A) plus 1
HLHHA + B

A plus (A + B) A plus (A+B) plus 1

LHHH A + B A plus (A + B

)A plus (A+B) plus 1

HHHH A A minus 1 A