**Lab 7: Adder Circuits**

**Introduction**

** **The heart if a computer
arithmetic unit is the adder circuit.
Two basic ways for carrying out addition are serial and parallel. Serial addition is carried out bit by bit
using a single full-adder circuit.
Parallel addition provides addition of all bits at the same time, which
is very fast, using a full-adder circuit for each bit position.

**Equipment**

Digital Breadboard

74LS08

74LS86

74LS83A

** Procedure**

1. Construct the circuit shown in Figure 1. Verify its operation by finding the truth
table for this circuit. Identify the A
and B as the Addend and Augend respectively.
Identify the outputs as the Sum and Carry out.

Figure
1

What kind of adder circuit is this? What is the purpose of the carry out output?

2. Construct the circuit shown in Figure 2. Notice this circuit employs an additional
input called the carry in. Verify the
proper operation of this circuit by creating a truth table for the circuit.

Figure
2

What kind of adder circuit is this? What is the purpose of the carry in
input? What are the differences between
the adders in figure 1 and 2?

3. Add a second full adder (Serial Adder) to the
circuit in figure 2 and describe its operation by making a truth table. Identify which full-adder sum is the LSB and
which is the MSB.

4. Use a 4-bit binary full-adder chip (74LS83A)
to make a 4-bit parallel full-adder.
Identify which inputs are the low-order bits.

Figure
3

How is a full-adder different from a
half-adder? What is the significance of
the carry-out of an adder unit? What
does “look-ahead adder circuitry do?