Specifications

Logic Devices 109
Adder/Incrementer
The N–bit Adder accepts one or two N–bit input arguments and (option-
ally) a 1–bit carry, and outputs their N–bit sum plus an optional 1–bit carry
out.
Multiple Adders can be connected together by feeding the Carry Out from
each stage to the Carry In of the next more significant stage. The Carry In
to the least significant stage should be set to zero.
Adder Pin Variations
The adder primitive can be used in four variations, as summarized in the
following table. Sample symbols are shown with 4–bit inputs, although any
number of bits from 1 to 256 is permissible.
In addition, the Carry Out pin can be independently included in, or omitted
from, any of these configurations.
 Refer to Appendix A, Primitive Device Pin Summary, for precise pin
order requirements.
Has B Inputs No B Inputs
Has Carry In S = A + B + Cin S = A + Cin
No Carry In S = A + B S = A + 1
LW Reference.bk Page 109 Monday, December 15, 2003 5:59 PM