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TASK – HALF ADDER TASK DESCRIPTION You will create a circuit that will add up two bits together. This is a famous circuit called a half
adder. THEORY We want a circuit
that will do the following additions: 0 + 0 = 00 0 + 1 = 01 1 + 0 = 01 1 + 1 = 10 So we want the two numbers in the addition to be inputs (A and
B). And, we want the answer, which is
two bits, to be two outputs. Traditionally, the outputs are labelled C and S (for Carry and
Sum). So we have A + B = CS. This gives us the following
truth table with two outputs C and S: A B C S 0 0 0 0 0 1 0 1 1 0 0 1 1 1 1 0 When we have two outputs,
we can express the truth tables separately.
This gives us two truth tables, one for output C: A B C 0 0 0 0 1 0 1 0 0 1 1 1 And another truth table for
output S: A B S 0 0 0 0 1 1 1 0
1 1 1 0 Now that we have truth
tables for each output, we simply have to figure out which gate(s) to use. For the truth table for
output C, you should be able to identify that it is the truth table of an AND
gate. For the truth table for
output S, you should be able to identify that it is the truth table of an XOR
gate. Therefore, a half adder is
created using an XOR gate and an AND gate. Below is the logic
diagram and a block diagram for a half adder.
So, addition in computers is done using
logic! Pretty cool! TASK Create a half adder circuit (seen above). It requires two light bulbs and you should
place the C light to the left of the S light so that it is natural to read
the combined output. TO SUBMIT One screen capture of your circuit. |
