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OR gate
From Wikipedia, the free encyclopedia
| INPUT A B |
OUTPUT A OR 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.
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There are two symbols for OR gates: the 'military' symbol and the 'rectangular' symbol. For more information see Logic Gate Symbols
OR Gates are basic logic gates, and as such they are recognised in TTL and CMOS ICs. The standard, 4000 series, CMOS IC is the 4071, which includes four independent, two-input, OR gates.
This device is available from most semiconductor manufacturers. It is usually available in both through-hole DIL and SOIC format. Datasheets are readily available in most Datasheet Databases.
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
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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
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.