7400 Series Guide: 74LS28 (Quad 2-input NOR gates)

The 74LS28 is a chip that has four basic NOR gates with buffered outputs. Buffered outputs means it can provide more current than a standard NOR gate in the 7400 series.

In this guide, you will learn everything you need to know about this chip and how you can use NOR gates in your own projects.

What does the 74HC28 / 74LS28 do?

The 74×28 gives you four basic NOR gates with buffered outputs that you can use individually. A NOR gate is a logic gate that outputs 1 (HIGH) if all of its inputs are 0 (LOW). In the truth table below, you can see what the output will be for any given input:

How To Use This Chip

The 74LS28 comes in a 14-pin package, and you need to connect it to power before you can use it. Like most 7400 ICs, it supports a VCC voltage of 5V.

The maximum current you can pull out of one output pin of the 74LS28 is 24 mA when the pin is low (sinking), but only 1.2 mA when the pin is high (sourcing). This can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, you can use any of the four NOR gates inside.

74LS28 Pinout

The 74LS28 has 14 pins and contains four basic NOR gates with buffered outputs laid out as shown in the pinout diagram below:

Pin #	Type	Description
1	Output	Output from the first NOR gate.
2	Input	Input to the first NOR gate.
3	Input	Input to the first NOR gate.
4	Output	Output from the second NOR gate.
5	Input	Input to the second NOR gate.
6	Input	Input to the second NOR gate.
7	Power	Connect to ground (GND).
8	Input	Input to the third NOR gate.
9	Input	Input to the third NOR gate.
10	Output	Output from the third NOR gate.
11	Input	Input to the fourth NOR gate.
12	Input	Input to the fourth NOR gate.
13	Output	Output from the fourth NOR gate.
14	Power	Positive power supply (VCC). Connect to +5V power.

Alternatives and Equivalents for 74LS28

The 74×28 chip exists in various versions. 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 (note that not all have actually been made):

• 74HC28 (High-speed CMOS)
• 74HCT28 (High-speed CMOS, TTL compatible)
• 74LS28 (High-speed TTL)
• 74LVC28 (Low Voltage TTL)
• 74AC28 (Advanced CMOS)
• 74ALS28 (Advanced Low-Power Schottky TTL)
• 74F28 (Very High Speed)
• 74C28 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the and SN74LS28 by Motorola.

Can’t find the 74×28 anywhere? Then try one of the following IC alternatives:

• 74×02 – Quad 2-input NOR gates
• 74×33 – Quad 2-input NOR gates (with open-collector outputs).
• 74×7002 – Quad 2-input NOR gates (with Schmitt-trigger inputs).
• CD4001 – Quad 2-input NOR gates

If you can’t find the 74×28 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 74LS28 chip

Download the PDF datasheet for the 74LS28 here:

• 74LS28 (Motorola)