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NOR gate
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NOR gate


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- the text and code below is from The Pseudopedia
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{{Unreferenced|date=December 2009}}{{about|NOR in the sense of an electronic logic gate (e.g. CMOS 4001)|NOR in the purely logical sense|Logical NOR|other uses of NOR or Nor|Nor}}{| class="wikitable" align=right bgcolor="#ddeeff" align="center"
A   B
A NOR B
INPUT OUTPUT
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- NorAdder.svg|thumb|right|150px|NOR Full adderFull adderThe NOR gate is a digital logic gate that implements logical NOR - it behaves according to the truth table to the right. A HIGH output (1) results if both the inputs to the gate are LOW (0). If one or both input is HIGH (1), a LOW output (0) results. NOR is the result of the negation of the OR operator. NOR is a functionally complete operation—combinations of NOR gates can be combined to generate any other logical function. By contrast, the OR operator is monotonic as it can only change LOW to HIGH but not vice versa.In most, but not all, circuit implementations, the negation comes for free—including CMOS and TTL. In such logic families, the only way to implement OR is with 2 or more gates, such as a NOR followed by an inverter. A significant exception is some forms of the domino logic family.

Symbols

There are three symbols for NOR 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.{| align=center style="text-align:center"|NOR ANSI Labelled.svg|NOR IEC.svg|NOR DIN.svg|MIL/ANSI Symbol|IEC Symbol|DIN Symbol

Hardware description and pinout

NOR Gates are basic logic gates, and as such they are recognised in TTL and CMOS ICs. The standard, 4000 series, CMOS IC is the 4001, which includes four independent, two-input, NOR gates. The pinout diagram is as follows:SS
8 Input A3
9 Input B3
10 Output Q3
11 Output Q4
12 Input B4
13 Input A4
14 VDD
NOR Pinout.jpg -
1 Input A1
2 Input B1
3 Output Q1
4 Output Q2
5 Input B2
6 Input A2
7 V

Availability

These devices are available from most semiconductor manufacturers such as Fairchild Semiconductor, Philips or Texas Instruments. These are usually available in both through-hole DIP and SOIC format. Datasheets are readily available in most datasheet databases.In the popular CMOS and TTL logic families, NOR gates with up to 8 inputs are available:
  • CMOS
    • 4001: Quad 2-input NOR gate
    • 4025: Triple 3-input NOR gate
    • 4002: Dual 4-input NOR gate
    • 4078: Single 8-input NOR gate
  • TTL
    • 7402: Quad 2-input NOR gate
    • 7427: Triple 3-input NOR gate
    • 7425: Dual 4-input NOR gate (with strobe, obsolete)
    • 74260: Dual 5-Input NOR Gate
    • 744078: Single 8-input NOR Gate
TTLright200px|The physical layoutphysical layoutThis diagrams above show the construction of a 2-input NOR gate using NMOS circuitry. If either of the inputs are high, the corresponding NMOS is turned on and the output is pulled low; otherwise the output is pulled high through the pull-up resistor. The diagram below shows a 2-input NOR gate using CMOS technology. The diodes and resistors on the inputs are to protect the CMOS components from damage due to electrostatic discharge (ESD) and play no part in the logical function of the circuit.Cmosunbuff.png -

Alternatives

frame|NOR Gate Constructed Using Only NAND Gatesframe|NAND Gate Constructed Using Only NOR GatesIf no specific NOR gates are available, one can be made from NAND gates in the configuration shown below. Interestingly, any logic gate can be made either from a combination of NAND gates or from a combination of NOR gates.

See also

{{Logical connectives}}NOR-GatterEZ-EDO ate logikoaNOR logicHradlo NOR

- content above as imported from The Pseudopedia
- "NOR gate" does not exist on GetWiki
- time: 3:58am EDT - Tue, Mar 16 2010