7400 Series Guide: 74HC85/74LS85 (4-bit magnitude comparator)

The 74×85 (ex 74HC85) is a cool little chip that has a 4-bit magnitude comparator. It let’s you compare two 4-bit numbers to see which is bigger (or if they’re equal).

In this guide, you will learn everything you need to know about this chip and how you can use magnitude comparators in your own projects.

What does the 74HC85 / 74LS85 do?

The 74×85 gives you a 4-bit magnitude comparator that you can to compare two 4-bit binary numbers.

It has three output signals:

• A < B: Logic high if A is less than B.
• A = B: Logic high if A is equal to B.
• A > B: Logic high if A is greater than B.

How To Use This Chip

The 74HC85 comes in a 16-pin package, and you need to connect it to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One difference between the HC and LS version of the chip is that the 74HC85 supports 2V to 6V, while the 74LS85 only supports 5V.

The maximum current you can pull out of one output pin on the 74HC85 chip is 4 mA. For the 74LS85 chip it’s 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, you can start comparing numbers by connecting the binary numbers to be compared to the A and B input pins. Based on the comparison, the relevant output pin (AB) will go high to indicate the result of the comparison.

74×85 Pinout

The 74×85 has 16 pins and contains 4-bit noninverting magnitude comparator with cascade inputs laid out as shown in the pinout diagram below:

Pin Name	Pin #	Type	Description
B3	1	Input	Most significant bit of the B input.
IA < B	2	Input	From previous stage: tie low if not used.
IA = B	3	Input	From previous stage: tie low if not used.
IA > B	4	Input	From previous stage: tie low if not used.
OA > B	5	Output	A > B output from the comparator.
OA = B	6	Output	A = B output from the comparator.
OA < B	7	Output	A < B output from the comparator.
GND	8	Power	Connect to ground (GND).
B0	9	Input	Least significant bit of the B input.
A0	10	Input	Least significant bit of the A input.
B1	11	Input	Second bit of the B input.
A1	12	Input	Second bit of the A input.
A2	13	Input	Third bit of the A input.
B2	14	Input	Third bit of the B input.
A3	15	Input	Most significant bit of the A input.
VCC	16	Power	Positive power supply (VCC). Connect to +5V power.

Alternatives and Equivalents for 74HC85 / 74LS85

There are many versions of the 74×85 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:

• 74HC85 (High-speed CMOS)
• 74HCT85 (High-speed CMOS, TTL compatible)
• 74LS85 (High-speed TTL)
• 74LVC85 (Low Voltage TTL)
• 74AC85 (Advanced CMOS)
• 74ALS85 (Advanced Low-Power Schottky TTL)
• 74F85 (Very High Speed)
• 74C85 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC85 and SN74LS85 by Texas Instruments.

Can’t find the 74×85 anywhere? Then try one of the following IC alternatives:

• 74×518 – 8-bit comparator (with open-collector outputs).
• 74×519 – 8-bit comparator (with open-collector outputs).
• 74×520 – 8-bit comparator, inverting output.
• 74×521 – 8-bit comparator, inverting output.
• 74×522 – 8-bit comparator, inverting output (with open-collector outputs).
• 74×524 – 8-bit registered comparator (with open-collector outputs).
• CD4063 – 4-bit magnitude comparator.
• CD4585 – 4-bit digital comparator.

If you can’t find the 74×85 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 74LS85 and 74HC85 chips

Download the PDF datasheet for your version of the 74×85 here:

• SN74LS85 (Texas Instruments)
• 74HC85 (Futurlec)
• 74LS85 (Futurlec)
• 74HC85 (Nexperia)