OR gate

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.

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. In another sense, the function of OR effectively finds the maximum between two binary digits, just as the complementary AND function finds the minimum.

Symbols

There are three symbols for OR gates: the American (ANSI or 'military') symbol and the IEC ('European' or 'rectangular') symbol, as well as the deprecated DIN symbol. For more information see Logic Gate Symbols.

MIL/ANSI Symbol	IEC Symbol	DIN 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. The traditional TTL version is the 7432. There are many offshoots of the original 7432 OR gate. All have the same pinout but different internal architecture, allowing them to operate in different voltage ranges and/or at higher speeds. In addition to the standard 2-Input OR Gate, 3- and 4-Input OR Gates are also available. In the CMOS series, these are:

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

TTL variations include:

• 74LS32: Quad 2-input OR gate (Low power Schottky version)
• 74HC32: Quad 2-input OR gate (High Speed CMOS version) - has lower current consumption/wider Voltage range
• 74LVC32: Low voltage CMOS version of the same.

Hardware description language

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

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

Wired OR gate using open-collector NOR gates

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.

See also

• AND gate
• NOT gate
• NAND gate
• NOR gate
• XOR gate
• Boolean algebra (logic)
• Logic gates