7400 Series Guide: 74LS55 (2-wide 4-input AND-NOR gate)

The 74×55 (ex 74LS55) is a chip with a 2-wide 4-input AND-NOR gate. This means there are two 4-input AND gates that go to a NOR gate.

In this guide, you’ll learn the things you need to know about this chip in order to use AND-NOR gates in your own projects.

What does the 74HC55 / 74LS55 do?

The 74LS55 gives you a 2-wide 4-input AND-NOR gate that you can use for digital logic circuits. An AND gate will output 1 (HIGH) if all of its inputs are 1 (HIGH). A NOR gate is a logic gate that outputs 1 (HIGH) if all of its inputs are 0 (LOW).

So to get a low output from this chip, all of the four inputs to one of the AND gates must be high.

How To Use This Chip

The 74LS55 comes in a 14-pin package, and you need to connect it to power before you can use it. Most versions of this chip supports a VCC voltage of 5V.

The maximum current you can pull out of the output pin is 0.4 mA when the pin is high (sourcing) or 8 mA when the pin is low (sinking). This can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, the 2-wide 4-input AND-NOR gate inside is functional.

74×55 Pinout

The 74×55 has 14 pins and contains a 2-wide 4-input AND-NOR gate with the pins laid out as shown in the pinout diagram below:

Pin #	Type	Description
1	Input	Input to the first AND gate.
2	Input	Input to the first AND gate.
3	Input	Input to the first AND gate.
4	Input	Input to the first AND gate.
5	NC	Not in use (Not Connected).
6	NC	Not in use (Not Connected).
7	Power	Connect to ground (GND).
8	Output	Output from the NOR gate.
9	NC	Not in use (Not Connected).
10	Input	Input to the second AND gate.
11	Input	Input to the second AND gate.
12	Input	Input to the second AND gate.
13	Input	Input to the second AND gate.
14	Power	Positive power supply (VCC). Connect to +5V power.

Alternatives and Equivalents for 74LS55

There are many versions of the 74×55 chip. They all have the same functionality, but with different specifications such as supported voltages and maximum current output.

Here’s a list of a few equivalents of this chip, although not all of them are necessarily in production:

• 74HC55 (High-speed CMOS)
• 74HCT55 (High-speed CMOS, TTL compatible)
• 74LS55 (High-speed TTL)
• 74LVC55 (Low Voltage TTL)
• 74AC55 (Advanced CMOS)
• 74ALS55 (Advanced Low-Power Schottky TTL)
• 74F55 (Very High Speed)
• 74C55 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74LS55 by Texas Instruments.

Can’t find the 74×55 anywhere? Then try one of the following IC alternatives:

• 74×50 – Dual 2-input AND-OR-Invert gate
• 74×51 – 2-Wide 2/3-input AND-NOR gate
• 74×54 – 4-Wide 2/3-input AND-NOR gate
• CD4085 – Dual 2-input AND-OR-Invert gate

If you can’t find the 74×55 IC in your local electronics store, don’t worry, you’ll most likely find it in one of the stores listed on this page of online stores where you’ll find components and tools for all your electronics projects.

Datasheet for the 74LS55 and 74HC55 chips

Download the PDF datasheet for your version of the 74×55 here:

• SN74LS55 (Texas Instruments)
• SN74LS55 (Motorola)