![Adder Adder](http://3.bp.blogspot.com/-6zNzvgvja8k/UeVUOXz84cI/AAAAAAAAAn8/Cc_yBOIBGU8/s1600/img7-16-2013-7.37.38+PM.jpg)
Aug 2, 2014 - This example describes a two input 4-bit adder/subtractor design in VHDL. The design unit multiplexes add and subtract operations with an OP.
Verilog Full Adder Example Full Adder We will continue to learn more examples with Combinational Circuit - this time a full adder. A combinational circuit is one in which the present output is a function of only the present inputs - there is no memory. This is different from the sequential circuits that we will learn later where the present output is a function of not only the present input but also of past inputs/outputs as well. Table: A one bit comparator Carry in Input y Input x Carry out Output A 0 0 0 0 0 0 0 1 0 1 0 1 0 0 1 0 1 1 1 0 1 0 0 0 1 1 0 1 1 0 1 1 0 1 0 1 1 1 1 1 Let us look at the source code for the implemmentation of a full adder fulladder.v.