This article is about NOR in the sense of an electronic logic gate (e.g. CMOS 4001). For NOR in the purely logical sense, see Logical NOR. For other uses of NOR or Nor, see Nor (disambiguation).
"4001" redirects here. For the year, see 5th millennium. For the ROM for the Intel 4004 processor, see Intel 4001.
The 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. It can also in some senses be seen as the inverse of an AND gate. NOR is a functionally complete operation—NOR gates can be combined to generate any other logical function. It shares this property with the NAND gate. 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, OR is the more complicated operation; it may use a NOR followed by a NOT. A significant exception is some forms of the domino logic family.
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. The ANSI symbol for the NOR gate is a standard OR gate with an inversion bubble connected. The bubble indicates that the function of the or gate has been inverted.
NOR Gates are basic logic gates, and as such they are recognised in TTL and CMOSICs. The standard, 4000 series, CMOS IC is the 4001, which includes four independent, two-input, NOR gates. The pinout diagram is as follows:
7425: Dual 4-input NOR gate (with strobe, obsolete)
74260: Dual 5-Input NOR Gate
744078: Single 8-input NOR Gate
In the older RTL and ECL families, NOR gates were efficient and most commonly used.
Implementationsedit
PMOS NOR gate with load resistor.
The diagrams above show the construction of a 2-input NOR gate using NMOS logic circuitry. If either of the inputs is high, the corresponding N-channel MOSFET 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.
The NOR gate has the property of functional completeness, which it shares with the NAND gate. That is, any other logic function (AND, OR, etc.) can be implemented using only NOR gates.[1] An entire processor can be created using NOR gates alone. The original Apollo Guidance Computer used 4,100 integrated circuits (IC), each one containing only two 3-input NOR gates.[2]
As NAND gates are also functionally complete, if no specific NOR gates are available, one can be made from NAND gates using NAND logic.[1]
^ abMano, M. Morris and Charles R. Kime. Logic and Computer Design Fundamentals, Third Edition. Prentice Hall, 2004. p. 73.
^Whipple, Walt (2019). First-Hand:Hacking Apollo's Guidance Computer. Engineering and Technology History Wiki.
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April 11, 2024
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This article is about NOR in the sense of an electronic logic gate e g CMOS 4001 For NOR in the purely logical sense see Logical NOR For other uses of NOR or Nor see Nor disambiguation 4001 redirects here For the year see 5th millennium For the ROM for the Intel 4004 processor see Intel 4001 This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources NOR gate news newspapers books scholar JSTOR September 2016 Learn how and when to remove this template message NOR gate truth tableInput OutputA B A NOR B0 0 10 1 01 0 01 1 0The 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 It can also in some senses be seen as the inverse of an AND gate NOR is a functionally complete operation NOR gates can be combined to generate any other logical function It shares this property with the NAND gate 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 OR is the more complicated operation it may use a NOR followed by a NOT A significant exception is some forms of the domino logic family Contents 1 Symbols 2 Hardware description and pinout 2 1 Availability 3 Implementations 4 Functional completeness 5 See also 6 ReferencesSymbols editThere 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 The ANSI symbol for the NOR gate is a standard OR gate with an inversion bubble connected The bubble indicates that the function of the or gate has been inverted nbsp nbsp nbsp MIL ANSI Symbol IEC Symbol DIN Symbol nbsp NOR Full adderHardware description and pinout editNOR 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 nbsp Pinout Diagram of a 4001 Quad NOR DIP format IC 1 Input A1 2 Input B1 3 Output Q1 4 Output Q2 5 Input B2 6 Input A2 7 Vss 8 Input A3 9 Input B3 10 Output Q3 11 Output Q4 12 Input B4 13 Input A4 14 VddAvailability edit 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 GateIn the older RTL and ECL families NOR gates were efficient and most commonly used Implementations edit nbsp nbsp PMOS NOR gate with load resistor The diagrams above show the construction of a 2 input NOR gate using NMOS logic circuitry If either of the inputs is high the corresponding N channel MOSFET is turned on and the output is pulled low otherwise the output is pulled high through the pull up resistor nbsp The physical layout of a CMOS NORThe 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 nbsp Unbuffered CMOS two input NOR gateFunctional completeness editMain article NOR logic The NOR gate has the property of functional completeness which it shares with the NAND gate That is any other logic function AND OR etc can be implemented using only NOR gates 1 An entire processor can be created using NOR gates alone The original Apollo Guidance Computer used 4 100 integrated circuits IC each one containing only two 3 input NOR gates 2 As NAND gates are also functionally complete if no specific NOR gates are available one can be made from NAND gates using NAND logic 1 Desired gate NAND Construction nbsp nbsp See also editAND gate OR gate NOT gate NAND gate XOR gate XNOR gate NAND logic Boolean algebra logic Flash memoryReferences edit a b Mano M Morris and Charles R Kime Logic and Computer Design Fundamentals Third Edition Prentice Hall 2004 p 73 Whipple Walt 2019 First Hand Hacking Apollo s Guidance Computer Engineering and Technology History Wiki nbsp Wikimedia Commons has media related to NOR gates Retrieved from https en wikipedia org w index php title NOR gate amp oldid 1202258187, 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