Quad Dual-Input NOR Gate ICs
Although the heading indicates 2-input NOR gates, this page covers all styles of NOR Gates.
Quad 2-Input NOR Gate Chip
The graphic shows the most common TTL Dual NOR Gate pinout  in a 14-pin DIP Package. A 4001 CMOS pin out in the same 14-pin DIP package is shown to the right. Many of these logic devices have alternate pin outs, although they were seldom used, they do exist and are available as a variant of the more general package. So in other words, only the common package pin out is ever shown here, with the understanding that other pin outs may exist.
NOR Gate by Function:
Each of the possible NOR gate functions are listed below; however not all the possible TTL Logic Families are listed.
Note in most cases when a TTL 74xx device is listed, a 54xx device may also be available. A few 5400 NOR gates are listed as examples. 74xx represents a commercial temperature range and 54xx represents the military temperature range [IC Temperature Prefixes] some 7400 TTL devices may also work within the industrial temperature range. The 54xx or 74xx part numbers are interchangeable here.
CMOS NOR Gates
4001; CMOS Quad 2-Input NOR Gate
4002; CMOS Dual 4-Input NOR Gate
4025; CMOS Triple 3-Input NOR Gate
4078; CMOS 8-Input NOR/OR Gate
TTL NOR Gates
7402; Quad 2-Input NOR Gate [NOR Gate w Totem-Pole Output]
7423; Dual 4-Input NOR Gates With Strobe, Expandable
7425; Dual 4-Input NOR Gates With Strobe
7427; Triple 3-Input NOR Gates
7433; Quad 2-Input Positive-NOR Buffers, Open-Collector Outputs
74805; Hex 2-Input NOR Drivers
74ALS1002; Quadruple 2-Input Positive-NOR Buffers
54HC02; High Speed CMOS Logic Quad 2-Input NOR Gates
54HC27; High Speed CMOS Logic Triple 3-Input NOR Gates
54HC4002; High Speed CMOS Logic Dual 4-Input NOR Gates
Editor note; check to see which sub-family is in production, a listing does not guarantee a device can be purchased..
The 4000 series NOR gates switch at CMOS levels which could be up to 15 volts, depending on the power supply [Vdd] used. While the 7400 series NOR gates switch at TTL Logic Levels. However a 74C02, 74HC02 are also CMOS gates with TTL compatible inputs and CMOS compatible outputs, and a 74HCT02 NOR gate is also a CMOS IC but with TTL compatible inputs and outputs. CMOS gates use CMOS FETs, while TTL gates use transistors to make up the internal structure.
NOR Gate True Table
A Strobe line is found on either the 5423 or 5427 NOR gates. The Strobe input forces the output of the NOR gate to go high when the strobe is low. The strobe input is used to 'strobe' or toggle the output. The strobe is indicated by the 1G and 2G inputs on the chip.
Dual 3-Input NOR Gate with Strobe
An expandable input allows additional gates to expand into the another gate. The incoming expander lines are tied to the outputs or the OR gate but before the input of the internal inverter.
Expandable 4-Input NOR Gate Chip
The internal schematic of a triple input NOR gate shown to the right is just one possible logic example, other internal designs are used. For example a 54S27 Schottky NOR gate would have the same pin out and true table output but a completely different internal structure, with the addition of Schottky diodes to prevent saturation.