MC74HC08AN: beginner guide to the Quad 2-input AND gate

The AND gate is one of the most fundamental building blocks of digital logic. Learn how the MC74HC08AN processes signals, understand its truth tables, and build a simple 5 V test circuit on a breadboard.

What is an AND gate?

An AND gate is a digital logic gate that performs a logical conjunction. It has two or more inputs and a single output. The output of an AND gate only goes HIGH (1) if and only if all of its inputs are HIGH (1). If any input is LOW (0), the output remains LOW (0).

The MC74HC08AN contains four independent 2-input AND gates in a single 14-pin DIP package. It is part of the high-speed CMOS (74HC) family, meaning it combines very low power consumption with high-speed performance, typically operating with a supply voltage from 2 V to 6 V.

MC74HC08AN: beginner-friendly 5 V AND-gate circuit
Functional overview; the numbered wiring list is the build instruction.

Understanding logic levels and thresholds

When operating at a 5 V supply (VCC = 5 V), the MC74HC08AN expects standard CMOS logic levels:

  • Input High (VIH): Minimum 3.5 V (0.7 × VCC). Any input voltage above this threshold is guaranteed to be recognized as a logical HIGH.
  • Input Low (VIL): Maximum 1.5 V (0.3 × VCC). Any input voltage below this threshold is recognized as a logical LOW.
  • Output High (VOH): Minimum 4.9 V under light load.
  • Output Low (VOL): Maximum 0.1 V under light load.

If you need to connect 3.3 V outputs (like those from a modern microcontroller) to 5 V logic, a standard 74HC chip might not reliably recognize 3.3 V as HIGH. In those cases, you should use a TTL-compatible alternative like the SN74AHCT08 AND-gate, which has lower input thresholds specifically designed for level translation.

Building a 5 V test circuit

MC74HC08AN PDIP-14 top view pinout showing four independent 2-input AND gates.
MC74HC08AN PDIP-14 top view pinout showing four independent 2-input AND gates.

To test the gate, we will wire up a simple circuit on a breadboard with two input switches and one indicator LED:

  1. Place the MC74HC08AN across the center division of your breadboard with the notch facing up/left. Use the separate top-view pinout above to identify the pins.
  2. Connect pin 14 (VCC) to the +5 V power rail. Connect pin 7 (GND) to the ground rail. Place a 100 nF ceramic capacitor directly between pins 14 and 7 to stabilize the power supply.
  3. Connect Switch A between +5 V and Pin 1 (Input 1A). Connect a 10 kΩ pull-down resistor from Pin 1 to GND. This ensures Pin 1 is pulled safely to 0 V when the switch is open.
  4. Connect Switch B between +5 V and Pin 2 (Input 1B). Connect a 10 kΩ pull-down resistor from Pin 2 to GND.
  5. Connect Pin 3 (Output 1Y) to the anode (longer leg) of an LED. Connect the cathode (shorter leg/flat side) of the LED to GND through a 330 Ω resistor to limit current.

First power-up and test

Apply 5 V DC to your breadboard power rails. When both switches are open, the LED remains off. Press Switch A alone or Switch B alone: the LED still remains off. Only when you press and hold both Switch A and Switch B simultaneously, both inputs go HIGH, the output pin 3 goes HIGH, and the LED lights up!

This simple logic function is the baseline for complex digital systems. For example, AND gates are used extensively for address decoding in retro computers to enable specific chips like the 74HC138 decoder or the CA82C55 programmable parallel I/O only when a specific address is accessed on the bus.

The stocked part and source

The stocked MC74HC08AN is a high-speed CMOS quad 2-input AND gate in a 14-pin plastic DIP package, manufactured by ON Semiconductor (formerly Motorola's semiconductor division), offering highly reliable operation for breadboard prototyping and retro projects.

View the MC74HC08AN product page · MC74HC08A datasheet