Philips Semiconductors
Product specification
4-bit arithmetic logic unit
FEATURES
•
Full carry look-ahead for high-speed arithmetic
operation on long words
•
Provides 16 arithmetic operations: add, subtract,
compare, double, plus 12 others
•
Provides all 16 logic operations of two variables:
EXCLUSIVE-OR, compare, AND, NAND, NOR, OR plus
10 other logic operations
•
Output capability:
•
I
CC
category: MSI
GENERAL DESCRIPTION
The 74HC/HCT181 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT181 are 4-bit high-speed parallel
Arithmetic Logic Units (ALU). Controlled by the four
function select inputs (S
0
to S
3
) and the mode control input
(M), they can perform all the 16 possible logic operations
or 16 different arithmetic operations on active HIGH or
active LOW operands (see function table).
When the mode control input (M) is HIGH, all internal
carries are inhibited and the device3 performs logic
operations on the individual bits as listed. When M is LOW,
the carries are enabled and the “181” performs arithmetic
operations on the two 4-bit words. The “181” incorporates
full internal carry look-ahead and provides for either ripple
carry between devices using the C
n+4
output, or for carry
look-ahead between packages using the carry
propagation (P) and carry generate (G) signals. P and
G are not affected by carry in.
ORDERING INFORMATION
TYPE
NUMBER
74HC181N3;
74HCT181N3
74HC181N;
74HCT181N
74HC181D;
74HCT181D
PACKAGE
NAME
DIP24
DIP24
SO24
DESCRIPTION
plastic dual in-line package; 24 leads (300 mil)
plastic dual in-line package; 24 leads (600 mil)
plastic small outline package; 24 leads; body width 7.5 mm
standard,
A=B open drain
74HC/HCT181
When speed requirements are not stringent, it can be used
in a simple ripple carry mode by connecting the carry
output (C
n+4
) signal to the carry input (C
n
) of the next unit.
For high-speed operation the device is used in conjunction
with the “182” carry look-ahead circuit. One carry
look-ahead package is required for each group of four
“181” devices. Carry look-ahead can be provided at
various levels and offers high-speed capability over
extremely long word lengths.
The comparator output (A=B) of the device goes HIGH
when all four function outputs (F
0
to F
3
) are HIGH and can
be used to indicate logic equivalence over 4 bits when the
unit is in the subtract mode. A=B is an open collector
output and can be wired-AND with other A=B outputs to
give a comparison for more than 4 bits. The open drain
output A=B should be used with an external pull-up
resistor in order to establish a logic HIGH level. 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 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
under-flow and no carry is generated when there is
underflow.
As indicated, the “181” 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.
VERSION
SOT222-1
SOT101-1
SOT137-1
1998 Jun 10
2
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