When different Logic Gates are connected they form a Logic Circuit. Logic Circuits are designed to perform a particular function.
Creating Truth Table for a Logic Circuit is a little more complicated than creating one for a simple Logic Gate ...
Add letters for the inputs to the circuit.
Label the output of each Logic Gate. This gives you the columns for your Truth Table.
Create the Truth Table for the circuit with one column for each letter you have used.
Start with Inputs A and B. Complete the table with the different input combinations.
Work out the different outputs from your first gate D
= A AND B.
Now start adding input C. To make things a little easier, we will assume C is 0 at the moment (we will change it to 1 later).
Now work out E = NOT C.
Now work out Q = D OR E.
Add four more rows to the table and copy the inputs for A, B and D down.
Add in the new values for C – 1 this time.
Work out the new values for E = NOT C.
Finally, work out the missing values for Q = D OR E.