The
NOR gate is a digital
logic gateA logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits...
that implements
logical NORIn boolean logic, logical nor or joint denial is a truth-functional 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 is an operation on propositions. For example, in classical logic negation is normally interpreted by the truth function that takes truth to falsity and vice versa...
of the
ORIn logic and mathematics, or, also known as logical disjunction or inclusive disjunction, is a logical operator 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 true. In grammar, or is a...
operator. NOR is a functionally complete operation -- combinations of NOR gates can be combined to generate any other logical function.
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 performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits...
that implements
logical NORIn boolean logic, logical nor or joint denial is a truth-functional 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 is an operation on propositions. For example, in classical logic negation is normally interpreted by the truth function that takes truth to falsity and vice versa...
of the
ORIn logic and mathematics, or, also known as logical disjunction or inclusive disjunction, is a logical operator 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 true. In grammar, or is a...
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, or, also known as logical disjunction or inclusive disjunction, is a logical operator 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 true. In grammar, or is a...
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 making integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data...
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 logicDomino logic is a CMOS-based evolution of the dynamic logic techniques which were based on either PMOS or NMOS transistors. It allows a rail-to-rail logic swing. It was developed to speed up circuits....
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
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.
 |
 |
image: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
CMOSComplementary metal–oxide–semiconductor is a technology for making integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data...
ICIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
s. The standard, 4000 series, CMOS IC is the 4001, which includes four independent, two-input, 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 SemiconductorPresent day Fairchild Semiconductor International, Inc. is a spin-off company resulting from reconstitution of assets in National Semiconductor. It inherits the Fairchild name of the original Fairchild Camera and Instrument Corporation, which had been the cornerstone of the semiconductor industry...
,
PhilipsKoninklijke Philips Electronics N.V. , most commonly known as Philips, is a Dutch electronics company.Philips is one of the largest electronics companies in the world. In 2007, its sales were €26.79 billion...
or
Texas InstrumentsTexas Instruments , widely known as TI, is an American company based in Dallas, Texas, United States, renowned for developing and commercializing semiconductor and computer technology. TI is the No. 4 manufacturer of semiconductors worldwide after Intel, Samsung and Toshiba, and is the top supplier...
. These are usually available in both through-hole
DIPIn microelectronics, a dual in-line package , sometimes called a DIL package, is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The pins are all parallel, point downward, and extend past the bottom plane of the package at least enough...
and
SOICA small-outline integrated circuit is a surface-mounted 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.
The standard 2-, 3-, 4- and 8-input NOR gates are available:
- CMOS
Complementary metal–oxide–semiconductor is a technology for making integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data...
- 4001: Quad 2-input NOR gate
- 4025: Triple 3-input NOR gate
- 4002: Dual 4-input NOR gate
- 4078: Mono 8-input 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 2-input NOR gate
- 7427: Triple 3-input NOR gate
- 7425: Dual 4-input NOR gate
- Mono 8-input NOR gate is not available in TTL
Implementations
This 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 resistorPull-up resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected...
. The diagram below shows a 2-input NOR gate using
CMOSComplementary metal–oxide–semiconductor is a technology for making integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data...
technology. The
diodeIn electronics a diode is a two-terminal electronic component which conducts electric current asymmetrically or unidirectionally; that is, it conducts current more easily in one direction than in the opposite direction. The term usually refers to a semiconductor diode, the most common type today,...
s and
resistor|- align = "center"||width = "25"|| |- align = "center"||| Potentiometer|- align = "center"| || |- align = "top"| Resistor|| Variable
resistor|- align = "center"||width = "25"|| |- align = "center"||| Potentiometer|- align = "center"...
s on the inputs are to protect the CMOS components from damage due to
electrostatic dischargeElectrostatic discharge is the sudden and momentary electric current that flows between two objects at different electrical potentials caused by direct contact or induced by an electrostatic field...
(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. Interestingly, 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, contrary to popular belief, 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 so-called "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, contrary to popular...
.
See also
- AND gate
The AND gate is a 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
PRASADThe 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 NAND gate is a digital logic gate that behaves in a manner that corresponds to the truth table to the left. A LOW output results only if both the inputs to the gate are HIGH. If one or both inputs are LOW, a HIGH output results...
- XOR gate
The XOR gate is a digital logic gate that implements exclusive disjunction - it behaves according to the truth table above. A HIGH output results if one, and only one, of the inputs to the gate is HIGH . If both inputs are LOW or both are HIGH , a LOW output results.XOR gate is short for...
- Boolean algebra (logic)
- Logic gates
- NOR logic
Like NAND gates, NOR gates are so-called "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, contrary to popular...