logic implementation with muxes

Thread Starter


Joined Apr 15, 2008
Hi, I have a question on how to implement a certain logic schematic.

I have to use 4 to 1 muxes to implement a full adder.

For the assignment I need to use 8 full adders to convert an 8 bit binary number to its 2s complement

I am mostly confused on how to implement the adder, can anyone help? I can probably get the rest once the adder is implemented.


Joined Feb 24, 2006
A single 4:1 Mux can implement any function of two boolean variables. You tie the 4 inputs to zero or one according to the function you are going to implement. The two boolean variables go to the select lines. Then what ever value the select lines take the correct value is routed to the output.

An adder is a combinatorial circuit. You start with a truth table
0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 0 plus a carry

So the boolean function for the sum is AB' + A'B which can also be written as A .xor. B

Clearly the boolean equation for the carry is A .and. B

Get the idea?