Full-Carry Look-Ahead Across the Four

Bits

Systems Achieve Partial Look-Ahead

Performance with the Economy of Ripple

Carry

Supply Voltage and Ground on Corner

Pins to Simplify P-C Board Layout

description

The *283 and 'LS283 adders are electrically and

functionally identical to the ‘B3A and 'LSB3A.

respectively; only the arrangement of the terminals

has been changed. The ‘S283 high performance

Versions are also functionally identical.

These improved full adders perform the addition of

two 4-bit binary words. The sum (Z) outputs are

provided for each bit and the resultant carry (C4) is

obtained from the fourth bit. These adders feature

full internal look-ahead across all four bits generating

the carry term in ten nanoseconds, typically, for the

283 and ‘LS283, and 7.5 nanoseconds for the ‘S283.

This capability provides the system designer with

partial look-ahead performance at the economy and

reduced package count of a ripple-carry

implementation.

The adder logic, including the carry, is implemented

in its true form. End around carry can be accomplish-

ed without the need for logic or level inversion.

Series 54, Series 54LS, and Series 54S circuits are

characterized for operation over the full temperature

range of 55°C to 125°C. Series 74, Series 74LS, and

Series 74S circuits are characterized for 0°C 10 70°C

operation.