A   B
0 0 1
0 1 0
1 0 0
1 1 1

The XNOR gate is a digital logic gate that impliments logical equality - it behaves according to the truth table to the right. A HIGH output (1) results if both of the inputs to the gate are the same. If one but not both inputs are HIGH (1), a LOW output (0) results.

Symbols Edit

There are two symbols for XNOR gates: the 'military' symbol and the 'rectangular' symbol. For more information see Logic Gate Symbols


'Military' XNOR Symbol


'Rectangular' XNOR Symbol

Hardware description and pinoutEdit

XNOR Gates are basic logic gates, and as such they are recognised in TTL and CMOS ICs. The standard, 4000 series, CMOS IC is the 4077, which includes four independent, two-input, XNOR gates. The pinout diagram is as follows:

File:XNOR Pinout.jpg
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

This device is available from most semiconductor manufacturers such as Philips. It is usually available in both through-hole DIL and SOIC format. Datasheets are readily available in most Datasheet Databases.

Alternatives Edit

If no specific XNOR gates are available, one can be made from five NAND gates in the configuration shown below. In fact, any logic gate can be made from combinations of only NAND gates or only NOR gates.

More Than Two Inputs Edit

Unlike AND/NAND and OR/NOR, the IEC symbol for an XNOR gate cannot be used as a base for producing wider XNOR functions simply by adding inputs, as this does not produce a logic function that matches common electronics industry usage. See XOR Gate for additional details.

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