OR gate: Definition from Answers.com

This article is about OR in the sense of an electronic logic gate (e.g. CMOS 4071). For OR in the purely logical sense, see Logical disjunction. For other uses of OR or Or, see Or (disambiguation).

INPUT A B		OUTPUT A + B
0	0	0
0	1	1
1	0	1
1	1	1

The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH (1). If neither input is HIGH, a LOW output (0) results.

1 Symbols
2 Hardware description and pinout
3 hardware description language
4 Implementations
- 4.1 Alternatives
5 Wired-OR
6 See also

Symbols

There are two symbols for OR gates: the 'military' symbol and the 'rectangular' symbol. For more information see Logic Gate Symbols

'American Standard' OR Symbol

'English Standard' OR Symbol

This schematic diagram shows the arrangement of OR gates within a standard 4071 CMOS integrated circuit.

Hardware description and pinout

OR Gates are basic logic gates, and as such they are available in TTL and CMOS ICs logic families. The standard, 4000 series, CMOS IC is the 4071, which includes four independent, two-input, OR gates. As well as the standard 2-Input OR Gate, 3- and 4-Input OR Gates are also available:

4075: Triple 3-Input OR Gate
4072: Dual 4-Input OR Gate

TTL:

74LS32: Quad 2-input OR gate

hardware description language

module(a,b,c); input a,b; output c; or (c,a,b); end module;

Implementations

CMOS OR Gate

Alternatives

OR Gate Constructed Using Only NAND Gates

If no specific OR gates are available, one can be made from NAND gates in the configuration shown below. Any logic gate can be made from a combination of NAND gates

Wired-OR

With active low open-collector logic outputs, as used for control signals in many circuits, an OR function can be produced by wiring together several outputs. This arrangement is called a wired OR. This implementation of an OR function typically is also found in integrated circuits of N or P-type only transistor processes.

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OR gate

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