Combinational logic example

- [Instructor] Now let's run a simulation … for a combinational circuit. … The system will simulate is the four-bit adder … I mentioned before. … It takes two four-bit numbers, A and B as inputs, … and it outputs a four-bit number, C, with a carry output … that serves as the 5th bit of this result. … This is a very popular combinational system … found in virtually every digital design book out there. … Notice how this four-bit adder … is composed of several smaller modules. … The logic here is the same as when you add numbers by hand. … First, at the bottom we have a half adder … that adds the least significant bits of A and B … which results in the least significant bit of C. … The half adder has a carry output … that is fed into a full adder, … which adds this carry input to bits A1 and B1. … This goes on and on for all bits in A and B. … Now, here we have the circuitry for the full adder module … which is a composition of two half adders and an OR gate. … So our system will consist on a series of nested …