Ben &Ethan's Digital Subtraction Page

Ben Ethan

Welcome to our page on logic gates and digital logic. We designed this web page as part of our final physics project at Etna Union High School. For our project, we researched digital logic, then designed and built a 3 bit digital subtracter.

---

Contents:

• Logic Gates
• Digital Subtraction Truth Table
• Digital "Half-subtracter" diagram
• Three bit subtracter plans
• Pictures of a 3 bit subtractor and a half adder on a solderless proto-board.

---

Logic Gates:

Logic gates are the basic building blocks of digital circuits. Listed below are several types and their characteristics. They take one or more inputs, and send out an output. They work in binary 1 (+ voltage) and 0 (Ground).

NOT Gate (Inverter) -

The not gate, or inverter, is the simplest logic gate, and has only one input and one output. It creates an output of 1 if the input is 0, and an output of 0 if the input is 1. It's symbol and truth table are shown below. Notice the circle below the triangle - this means the output is inverted.

Input	Output
0	1
1	0

AND Gate -

The AND gate checks two input signals. If both of the signals are 1, than it produces an output of 1. Otherwise, it produces an output of 0.

Input 1	Input 2	Output
0	0	0
0	1	0
1	0	0
1	1	1

OR Gate-

The OR gate produces an output of 1 if EITHER of the inputs are 1. A normal OR gate produces an output of 1 if both inputs are 1 also.

Input 1	Input 2	Output
0	0	0
0	1	1
1	0	1
1	1	1

XOR Gate-

The XOR is similar to the OR gate in that it produces an output of 1 if EITHER of the inputs are 1. However the XOR (eXclusive OR) will not produce an output of 1 if both of the inputs are 1.

Input 1	Input 2	Output
0	0	0
0	1	1
1	0	1
1	1	0

NAND Gate-

The NAND gate is the opposite of an AND gate. As long as both of the inputs are not 1, it produces and output of 1. Notice that its symbol is the same as that of the AND gate except for the circle at the bottom, which means inverted.

Input 1	Input 2	Output
0	0	1
0	1	1
1	0	1
1	1	0

NOR Gate-

The NOR gate is the opposite of an OR gate. It only produces an output of 1 if neither of the input signals are 1.

Input 1	Input 2	Output
0	0	1
0	1	0
1	0	0
1	1	0

If you have any comments, questions, or anything else to say to us, E-MAIL us at

or