74LS00 (7400) Logic Gate - NAND, Pinout, and Applications

The 74LS00 (also known as 7400) is a TTL integrated circuit that contains four independent two-input NAND logic gates. It is powered with +5V (4.75–5.25V), and each gate performs the Boolean operation Y = (A·B)'. The output is "0" (LOW) only when both inputs are "1" (HIGH). In any other case, the output is "1".

This component is extremely popular because the NAND gate is "universal," meaning it can be used to build any other logic function (AND, OR, NOT, etc.), making it a fundamental piece in digital electronics.

What is the 74LS00?

The 74LS00 is a quad low-power NAND gate (LS series). Its main features are:

Four independent two-input NAND gates.
Low power consumption and high speed.
Compatible with standard TTL logic levels (5V).
It is one of the most versatile and widely used logic gates.

Basic Operation and Truth Table

Each NAND gate in the 74LS00 functions as an AND gate followed by an inverter (NOT). The output is the negation of the result of an AND operation.

Truth table for each NAND gate:

Input A	Input B	Output Y
0	0	1
0	1	1
1	0	1
1	1	0

Internal operation: It uses low-power Schottky TTL technology for fast switching, with a typical propagation delay of about 10 ns.

Pinout and Connections

The 74LS00 comes in a 14-pin DIP package, identical in configuration to the 7408 (AND) and 7432 (OR):

Pin 7: GND (Ground)
Pin 14: VCC (+5V)
Gates organized as follows:
- Gate 1: Inputs (Pin 1, 2), Output (Pin 3)
- Gate 2: Inputs (Pin 4, 5), Output (Pin 6)
- Gate 3: Inputs (Pin 9, 10), Output (Pin 8)
- Gate 4: Inputs (Pin 12, 13), Output (Pin 11)

Detailed Technical Specifications

Specification	Parameter (74LS00)
Logic Function	NAND
Number of gates	4 (Quad)
Inputs per gate	2
Supply Voltage	4.75 – 5.25 V
Technology	TTL 74LS family (LS-TTL)
Output Current (I_OL)	up to 8 mA (low level)
Output Current (I_OH)	–0.4 mA (high level)
Typical Delay (t_pd)	~10 ns (propagation)
Operating T_range	0 °C to 70 °C

Component Variants

SN7400/SN74LS00: Standard and low-power TTL versions.
SN74HC00: High-speed CMOS version, operates from 2V to 6V.
SN74HCT00: CMOS version with TTL-compatible inputs.
Other variants: 74F00 (Very High-Speed), 74S00 (Schottky).

Practical Applications and Universality

The NAND gate is universal, which means you can create any other logic gate using only NANDs:

Inverter (NOT): By connecting the two inputs of a NAND gate together.
AND Gate: Using a NAND gate followed by an inverter (which is another NAND).
OR Gate: Using three NAND gates.

Use cases:

Control logic: Implementing any Boolean function.
Oscillators and Flip-Flops: Building basic memory circuits (like an SR flip-flop) and clock generators.
Alarm systems: Activating an alarm when a condition is not met (e.g., the door is not closed AND the system is not deactivated).

Practical Resources

Datasheet SN74LS00 (Texas Instruments): [Quad 2-Input NAND Gates]
Datasheet SN74HC00 (Texas Instruments): [Quad 2-Input NAND Gates - CMOS]
Simulations: Tinkercad, Falstad, and other simulators are ideal for experimenting with the universality of the NAND gate.

Frequently Asked Questions (FAQ)

What gate is the 7400? The 7400 (or 74LS00) is an integrated circuit containing four two-input NAND logic gates.

What is the truth table for the 7400? The output is 0 only when both inputs are 1. For all other combinations (0-0, 0-1, 1-0), the output is 1.

What does the 7400 integrated circuit do? It performs the NAND (negated AND) logic operation. It is a universal gate, allowing any other logic function to be built from it.

What voltage does the 74LS00 operate at? It operates at a standard TTL voltage of 5V (range 4.75–5.25V).

How do you make a NOT gate with a NAND? To create an inverter (NOT), simply connect the two inputs of a NAND gate together. The output will be the negation of the single input signal.

What do SN74LS00, 74HC00, etc., mean? They are different logic families: 74LS00 (TTL Low-Power Schottky), 74HC00 (High-speed CMOS), and 74HCT00 (CMOS with TTL-compatible inputs). All perform the NAND function but with different electrical characteristics.

References: Information is based on official datasheets from Texas Instruments and digital electronics technical guides.