Question

Using the full adder already designed as a block, design an 8-bit ripple carry adder.

a) Add 3 splitters to the circuit. Each splitter should have an input width of 8 bits and a fan out of 8.
b) Attach two east-facing splitters to the 8-bit inputs A and B.
c) Attach a west-facing splitter to the 8-bit output S.
d) Create eight instances of the FA circuit.
e) Connect the S outputs of the eight FA instances to the splitter for the 8-bit S output.
f) Connect the carry inputs and outputs of the eight FA instances so that carries will propagate appropriately from the Ci input, through the 1-bit adders, to the Co output.
g) Connect the A inputs of the eight FA instances to the splitter for the A input.
h) Connect the B inputs of the eight FA instances to the splitter for the B input.
i) Test your circuit.
Solve this question using Logisim!

Answer 1

The design of an 8-bit ripple carry adder on Logisim involves using full adder blocks connected to splitters managing the input and output bits, ensuring that the carry propagates appropriately through all eight stages of the adder.

Step-by-step explanation:

The question involves designing an 8-bit ripple carry adder using a circuit simulation tool known as Logisim, which falls under the subject of Computers and Technology at a College level. The adder sums two 8-bit inputs to produce an 8-bit output with the potential for a carryout bit. In Logisim, this involves connecting multiple full adder (FA) blocks, commonly used in digital electronics.

To accomplish the task, you need to:

Add three splitters to handle the 8-bit wide input and output buses.

Connect the input splitters to the 8-bit input signals, A and B, respectively, and the output splitter to the 8-bit output S.

Create and connect eight instances of the full adder block, with each one taking a single bit from both the A and B splitters and chaining the carry output to the next adder's carry input, with the first FA's carry input connected to the initial carry-in (Ci) signal and the last FA's carry output as the final carry-out (Co).

1. Finally, connect each full adder's sum output (S) to the corresponding input bit of the output splitter.

Upon completion, testing the circuit involves providing various 8-bit values for A and B and verifying that the sum (S) and carry out (Co) are correct. This process confirms that the ripple effect of the carriers is properly managed throughout the adder chain.