INPUT A B 
OUTPUT A NOR B 
0 
0 
1 
0 
1 
0 
1 
0 
0 
1 
1 
0 
The
NOR gate is a digital
logic gateA logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
that implements
logical NORIn boolean logic, logical nor or joint denial is a truthfunctional operator which produces a result that is the negation of logical or. That is, a sentence of the form is true precisely when neither p nor q is true—i.e. when both of p and q are false...
 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
negationIn logic and mathematics, negation, also called logical complement, is an operation on propositions, truth values, or semantic values more generally. Intuitively, the negation of a proposition is true when that proposition is false, and vice versa. In classical logic negation is normally identified...
of the
ORIn logic and mathematics, a twoplace logical connective or, is a logical disjunction, also known as inclusive disjunction or alternation, that results in true whenever one or more of its operands are true. E.g. in this context, "A or B" is true if A is true, or if B is true, or if both A and B are...
operator. NOR is a functionally complete operation—combinations of NOR gates can be combined to generate any other logical function. By contrast, the
ORIn logic and mathematics, a twoplace logical connective or, is a logical disjunction, also known as inclusive disjunction or alternation, that results in true whenever one or more of its operands are true. E.g. in this context, "A or B" is true if A is true, or if B is true, or if both A and B are...
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
CMOSComplementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
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 logicDomino logic is a CMOSbased evolution of the dynamic logic techniques which were based on either PMOS or NMOS transistors. It allows a railtorail logic swing. It was developed to speed up circuits....
family.
The original
Apollo Guidance ComputerThe Apollo Guidance Computer provided onboard computation and control for guidance, navigation, and control of the Command Module and Lunar Module spacecraft of the Apollo program...
used 4,100 ICs, each one containing only a single 3input NOR gate.
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
DINDIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....
symbol. For more information see Logic Gate Symbols.



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
CMOSComplementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
ICAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s. The standard, 4000 series, CMOS IC is the 4001, which includes four independent, twoinput, NOR gates. The pinout diagram is as follows:

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 VDD

Availability
These devices are available from most semiconductor manufacturers such as
Fairchild SemiconductorFairchild Semiconductor International, Inc. is an American semiconductor company based in San Jose, California. Founded in 1957, it was a pioneer in transistor and integrated circuit manufacturing...
,
PhilipsKoninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
or
Texas InstrumentsTexas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
. These are usually available in both throughhole
DIPIn microelectronics, a dual inline package is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be throughhole mounted to a printed circuit board or inserted in a socket.A DIP is usually referred to as a DIPn, where n is...
and
SOICA smalloutline integrated circuit is a surfacemounted integrated circuit package which occupies an area about 30–50% less than an equivalent DIP, with a typical thickness that is 70% less. They are generally available in the same pinouts as their counterpart DIP ICs...
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
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
 4001: Quad 2input NOR gate
 4025: Triple 3input NOR gate
 4002: Dual 4input NOR gate
 4078: Single 8input NOR gate
 TTL
Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...
 7402: Quad 2input NOR gate
 7427: Triple 3input NOR gate
 7425: Dual 4input NOR gate (with strobe, obsolete)
 74260: Dual 5Input NOR Gate
 744078: Single 8input NOR Gate
In the older RTL and
ECLIn electronics, emittercoupled logic , is a logic family that achieves high speed by using an overdriven BJT differential amplifier with singleended input, whose emitter current is limited to avoid the slow saturation region of transistor operation....
families, NOR gates were efficient and most commonly used.
Implementations
This diagrams above show the construction of a 2input NOR gate using
NMOS logicNtype metaloxidesemiconductor logic uses ntype metaloxidesemiconductor field effect transistors to implement logic gates and other digital circuits...
circuitry. If either of the inputs are high, the corresponding Nchannel
MOSFETThe metal–oxide–semiconductor fieldeffect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
is turned on and the output is pulled low; otherwise the output is pulled high through the
pullup resistorPullup resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected or highimpedance...
. The diagram below shows a 2input NOR gate using
CMOSComplementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
technology. The
diodeIn electronics, a diode is a type of twoterminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
s and
resistorA linear resistor is a linear, passive twoterminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
s on the inputs are to protect the CMOS components from damage due to
electrostatic dischargeElectrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
(ESD) and play no part in the logical function of the circuit.
Alternatives
If no specific NOR gates are available, one can be made from NAND gates in the configuration shown below. Any logic gate can be made either from a
combination of NAND gatesNAND gates are one of the two basic logic gates from which any other logic gates can be built. Due to this property, NAND and NOR gates are sometimes called "universal gates". However, modern integrated circuits are not constructed exclusively from a single type of gate...
or from a
combination of NOR gatesLike NAND gates, NOR gates are socalled "universal gates" that can be combined to form any other kind of logic gate. For example, the first embedded system, Apollo Guidance Computer, was built exclusively from NOR gates, about 5,600 in total for the later versions. Today, integrated circuits are...
.
See also
 AND gate
The AND gate is a basic digital logic gate that implements logical conjunction  it behaves according to the truth table to the right. A HIGH output results only if both the inputs to the AND gate are HIGH . If neither or only one input to the AND gate is HIGH, a LOW output results...
 OR gate
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 results if one or both the inputs to the gate are HIGH . If neither input is HIGH, a LOW output results...
 NOT gate
 NAND gate
The Negated AND, NO AND or NAND gate is the opposite of the digital AND gate, and behaves in a manner that corresponds to the opposite of AND gate, as shown in the truth table on the right. A LOW output results only if both the inputs to the gate are HIGH...
 XOR gate
The XOR gate is a digital logic gate that implements an exclusive or; that is, a true output results if one, and only one, of the inputs to the gate is true . If both inputs are false or both are true , a false output results. Its behavior is summarized in the truth table shown on the right...
 Boolean algebra (logic)
 Logic gates
 NOR logic
Like NAND gates, NOR gates are socalled "universal gates" that can be combined to form any other kind of logic gate. For example, the first embedded system, Apollo Guidance Computer, was built exclusively from NOR gates, about 5,600 in total for the later versions. Today, integrated circuits are...