LOGIC UNIT. SN54LS181 Datasheet 


4BIT ARITHMETIC
LOGIC UNIT
The SN54 / 74LS181 is a 4bit Arithmetic Logic Unit (ALU) which can
perform all the possible 16 logic, operations on two variables and a variety of
arithmetic operations.
• Provides 16 Arithmetic Operations Add, Subtract, Compare, Double,
Plus Twelve Other Arithmetic Operations
• Provides all 16 Logic Operations of Two Variables Exclusive — OR,
Compare, AND, NAND, OR, NOR, Plus Ten other Logic Operations
• Full Lookahead for High Speed Arithmetic Operation on Long Words
• Input Clamp Diodes
CONNECTION DIAGRAM DIP (TOP VIEW)
VCC A1 B1 A2 B2 A3 B3 G Cn+4 P A=B F3
24 23 22 21 20 19 18 17 16 15 14 13
1 2 3 4 5 6 7 8 9 10 11 12
B0 A0 S3 S2 S1 S0 Cn M F0 F1 F2 GND
NOTE:
The Flatpak version
has the same pinouts
(Connection Diagram) as
the Dual InLine Package.
PIN NAMES
LOADING (Note a)
HIGH
LOW
A0 – A3, B0 – B3
S0 – S3
M
Cn
F0 – F3
A=B
G
P
Cn+4
Operand (Active LOW) Inputs
Function — Select Inputs
Mode Control Input
Carry Input
Function (Active LOW) Outputs
Comparator Output
Carry Generator (Active LOW)
Output
Carry Propagate (Active LOW)
Output
Carry Output
1.5 U.L.
2.0 U.L.
0.5 U.L.
2.5 U.L.
10 U.L.
Open Collector
10 U.L.
10 U.L.
10 U.L.
0.75 U.L.
1.0 U.L.
0.25 U.L.
1.25 U.L.
5 (2.5) U.L.
5 (2.5) U.L.
10 U.L.
5 U.L.
5 (2.5) U.L.
NOTES:
a. 1 TTL Unit Load (U.L.) = 40 µA HIGH/1.6 mA LOW.
b. The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74)
b. Temperature Ranges.
SN54/74LS181
4BIT ARITHMETIC
LOGIC UNIT
LOW POWER SCHOTTKY
24
1
J SUFFIX
CERAMIC
CASE 62305
24
1
N SUFFIX
PLASTIC
CASE 64903
ORDERING INFORMATION
SN54LSXXXJ Ceramic
SN74LSXXXN Plastic
LOGIC SYMBOL
2 1 23 22 21 20 19 18
A0 B0 A1 B1 A2 B2 A3 B3
7 Cn
Cn+4
16
8M
A=B
14
6 S0
G 17
5 S1
4 S2
P 15
3 S3 F0 F1 F2 F3
9 10 11 13
VCC = PIN 24
GND = PIN 12
FAST AND LS TTL DATA
5332

SN54 / 74LS181
LOGIC DIAGRAM
782
Cn M A0
1 23
B0 A1
22 21
B1 A2
20 19
B2 A3
18
B3
S0
6
S1
5
S2
4
S3
3
F0 F1 A = B F2
9 10 14 11
VCC = PIN 24
GND = PIN 12
= PIN NUMBERS
F3
13
P Cn+4 G
15 16
17
FUNCTIONAL DESCRIPTION
The SN54 / 74LS181 is a 4bit high speed parallel Arithmetic
Logic Unit (ALU). Controlled by the four Function Select Inputs
(S0 . . . S3) and the Mode Control Input (M), it can perform all
the 16 possible logic 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 performs logic operations
on the individual bits as listed. When the Mode Control Input is
LOW, the carries are enabled and the device performs
arithmetic operations on the two 4bit words. The device
incorporates full internal carry lookahead and provides for
either ripple carry between devices using the Cn+4 output, or
for carry lookahead between packages using the signals P
(Carry Propagate) and G (Carry Generate), P and G are not
affected by carry in. When speed requirements are not
stringent, the LS181 can be used in a simple ripple carry mode
by connecting the Carry Output (Cn+4) signal to the Carry Input
(Cn) of the next unit. For high speed operation the LS181 is
used in conjunction with the 9342 or 93S42 carry lookahead
circuit. One carry lookahead package is required for each
group of the four LS181 devices. Carry lookahead can be
provided at various levels and offers high speed capability
over extremely long word lengths.
The A = B output from the LS181 goes HIGH when all four F
outputs are HIGH and can be used to indicate logic
equivalence over four bits when the unit is in the subtract
mode. The A = B output is open collector and can be
wiredAND with other A = B outputs to give a comparison for
more then four bits. The A = B signal can also be used with the
Cn+4 signal to indicate A>B and A<B.
The Function Table lists the arithmetic operations that are
performed without a carry in. An incoming carry adds a one to
each operation. Thus, select code LHHL generates A minus B
minus 1 (2s complement notation) without a carry in and
generates A minus B when a carry is applied. Because
subtraction is actually performed by complementary addition
(1s complement), a carry out means borrow; thus a carry is
generated when there is no underflow and no carry is
generated when there is underflow.
As indicated, the LS181 can be used with either active LOW
inputs producing active LOW outputs or with active HIGH
inputs producing active HIGH outputs. For either case the
table lists the operations that are performed to the operands
labeled inside the logic symbol.
FAST AND LS TTL DATA
5333

SN54 / 74LS181
FUNCTION TABLE
MODE SELECT
INPUTS
ACTIVE LOW INPUTS
& OUTPUTS
S3 S2 S1 S0
LOGIC
(M = H)
ARITHMETIC**
(M = L) (Cn = L)
L L L LA
A minus 1
L L L H AB
AB minus 1
L L H L A+B
AB minus 1
L L H H Logical 1 minus 1
L H L L A+B
A plus (A + B)
L H L HB
AB plus (A + B)
L H H L A⊕B
A minus B minus 1
L H H H A+B
A+B
H L L L AB
A plus (A + B)
H L L H A⊕B
A plus B
H L H LB
AB plus (A + B)
H L H H A+B
A+B
H H L L Logical 0 A plus A*
H H L H AB
AB plus A
H H H L AB
AB plus A
H H H HA
A
L = LOW Voltage Level
H = HIGH Voltage Level
**Each bit is shifted to the next more significant position
**Arithmetic operations expressed in 2s complement notation
ACTIVE HIGH INPUTS
& OUTPUTS
LOGIC
(M = H)
ARITHMETIC**
(M = L) (Cn = H)
AA
A+B
A+B
AB A + B
Logical 0 minus 1
AB A plus AB
B (A + B) plus AB
A⊕B
A minus B minus 1
AB AB minus 1
A+B
A plus AB
A⊕B
A plus B
B (A + B) plus AB
AB AB minus 1
Logical 1 A plus A*
A+B
(A + B) plus A
A+B
(A + B) Plus A
A A minus 1
LOGIC SYMBOLS
ACTIVE LOW OPERANDS
2 1 23 22 21 20 19 18
A0 B0 A1 B1 A2 B2 A3 B3
7 Cn
Cn+4
16
8M
LS181
A=B
14
6 S0 4 BIT ARITHMETIC G 17
5 S1
4 S2
LOGIC UNIT
P 15
3 S3 F0 F1 F2 F3
9 10 11 13
ACTIVE HIGH OPERANDS
2 1 23 22 21 20 19 18
A0 B0 A1 B1 A2 B2 A3 B3
7 Cn
Cn+4
16
8M
LS181
A=B
14
6 S0 4 BIT ARITHMETIC G 17
5 S1
4 S2
LOGIC UNIT
P 15
3 S3 F0 F1 F2 F3
9 10 11 13
GUARANTEED OPERATING RANGES
Symbol
Parameter
VCC
Supply Voltage
TA Operating Ambient Temperature Range
IOH Output Current — High
IOL Output Current — Low
VOH
Output Voltage — High (A = B only)
Min Typ Max Unit
54 4.5 5.0 5.5
74 4.75 5.0 5.25
V
54 – 55 25 125 °C
74 0 25 70
54, 74
– 0.4
mA
54 4.0 mA
74 8.0
54, 74
5.5 V
FAST AND LS TTL DATA
5334

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