Week 1: Combinational Circuits Flashcards
What function does the OR Gate have in a full adder?
The OR gate is connected to the AND gates of the 2 half adders. The AND gates will tell us either or not there’s a carry bit.
In the case the one of the half adders or both have a carry bit, the OR gate ensures that a 1 will be produced as the carry out bit.
What does an XOR give as an output?
The sum/result of the bits.
What does an AND gate give as an output?
The carry out bit. This can then be linked to another half adder to continue adding bigger binary numbers together.
What is the function of a combinational circuit?
They’re like functions in programming where we can call on them to do a task many times within a system.
It also makes sure that we’re not using the same circuits over and over again.
What are the main differences & similarities between a full and half adder?
- Half adder only adds 2 bits, full adder does 3 (2 inputs vs 3 inputs)
- Both of them have 2 outputs
Why do we need a full adder?
A half adder is only able to add 2 bits together. If we were to add a third bit as a carry-in bit, we would need to use another half adder. This in turn would make a full adder circuit.
What do XOR gates do in a full adder?
They complete binary addition for us. If both numbers are the same, we get an output of 0 which allows us to have a carry bit.
What do AND gates do in a full adder?
They check to see if we have a carry bit or not. This is done by checking if both bits are 1 and if that’s the case they’ll be moved onto the carry out bit output.
