7400 Series Guide: 74HC126/74LS126 (3-state buffers)

The 74×126 (ex 74HC126) is a chip that contains four tri-state buffers, each with independent enable control.

In this guide, you’ll learn the things you need to know about this chip in order to use tri-state buffers in your own projects.

What does the 74HC126 / 74LS126 do?

The 74×126 is a quad buffer with tri-state outputs. It means there are four individual buffer gates inside the chip.

A buffer is a logic gate that takes an input signal and passes it directly to its output, providing signal amplification or isolation without changing the signal’s logic state.

Each buffer has a separate enable input. When the enable input is LOW, the buffer disconnects its output, placing it in a high-impedance (Hi-Z) state. When the enable input is HIGH, the buffer actively passes the input signal to the output.

The tri-state feature is handy for connecting multiple devices to a single data line, ensuring that only one device drives the line at a time. This is useful for bus systems in digital circuits.

How To Use This Chip

The 74HC126 comes in a 14-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 74HC126 supports 2V to 6V, while the 74LS126 only supports 5V.

74HC chips can normally supply a maximum of 4 mA from an output pin. If you’re using the 74LS version, the maximum current you can pull out of one output pin is 0.4 mA when the pin is high (sourcing) or 8 mA when the pin is low (sinking).

But these values can differ between models, so check the datasheet of your model to verify.

Once you’ve connected it to power, you can use the Tri-state buffers inside.

74×126 Pinout

The 74×126 has 14 pins and contains four 3-state buffers laid out as shown in the pinout diagram below:

Pin Name	Pin #	Type	Description
1OE	1	Input	Output Enable for the first Tri-state buffer.
1A	2	Input	Input to the first Tri-state buffer.
1Y	3	Output	Output from the first Tri-state buffer.
2OE	4	Input	Output Enable for the second Tri-state buffer.
2A	5	Input	Input to the second Tri-state buffer.
2Y	6	Output	Output from the second Tri-state buffer.
GND	7	Power	Connect to ground (GND).
3Y	8	Output	Output from the third Tri-state buffer.
3A	9	Input	Input to the third Tri-state buffer.
3OE	10	Input	Output Enable for the third Tri-state buffer.
4Y	11	Output	Output from the fourth Tri-state buffer.
4A	12	Input	Input to the fourth Tri-state buffer.
4OE	13	Input	Output Enable for the fourth Tri-state buffer.
VCC	14	Power	Positive power supply. Connect to +5V power.

Alternatives and Equivalents for 74HC126 / 74LS126

There are many versions of the 74×126 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:

• 74HC126 (High-speed CMOS)
• 74HCT126 (High-speed CMOS, TTL compatible)
• 74LS126 (High-speed TTL)
• 74LVC126 (Low Voltage TTL)
• 74AC126 (Advanced CMOS)
• 74ALS126 (Advanced Low-Power Schottky TTL)
• 74F126 (Very High Speed)
• 74C126 (CMOS, similar to the 4000-series)

Some manufacturers also add a prefix, such as the SN74HC126 and SN74LS126 by Texas Instruments.

Can’t find the 74×126 anywhere? Then try one of the following IC alternatives:

• 74×125 – Quad 3-state buffer.
• 74×241 – Octal buffer/line driver with 3-state outputs.
• 74×244 – Octal buffer/line driver with 3-state outputs (non-inverting).
• 74×365 – Hex buffer/line driver with 3-state outputs.
• 74×367 – Hex buffer/line driver with 3-state outputs (non-inverting).
• CD4503 – Hex non-inverting 3-state buffer.

If you can’t find the 74×126 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 74LS126 and 74HC126 chips

Download the PDF datasheet for your version of the 74×126 here:

• SN74HC126 (Texas Instruments)
• 74HC126 (Futurlec)
• 74LS126 (Futurlec)
• 74HC126 (Diodes Inc)
• 74HC126 (Nexperia)