1-bit adders

A 1-bit adder circuit accepts two 1-bit binary numbers and a carry input and outputs a 1-bit sum and a carry.
The next table shows the truth table for a 1-bit adder.

Table 1: Truth table for a 1-bit adder
Input1	Input0	Carry Input	Sum Output	Carry Output
0	0	0	0	0
0	0	1	1	0
0	1	0	1	0
0	1	1	0	1
1	0	0	1	0
1	0	1	0	1
1	1	0	0	1
1	1	1	1	1

The logic circuitry for a 1-bit adder is shown in the following figure.
These are the instructions to play with the circuit:

Click on the 1's and 0's in green (the inputs) to change their value. To run the simulation with these new values, click on the "Continue" value.

Click on any of the logic gates and its output value will appear in the "Block value" box.

The "Reset" button will clear all the input values.

This circuit can be encapsulated in a single module, as can be seen in the following figure :

A 4 - bit adder circuit is constructed in the next page.

Last modified 2/1/2000 by Juan de Lara ( Juan.Lara@ii.uam.es, http://www.ii.uam.es/~jlara) need help for using this courses?.

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