The 74×266 (ex 74HC266) is a chip with four open-collector XNOR gates. Open-collector outputs make it simple to connect to other chips that use different logic levels. But it also means you can’t use this chip as a direct replacement for a normal XNOR gate chip.
In this guide, you will learn all about this chip and how you can use its XNOR gates in your own circuit.
What does the 74HC266 / 74LS266 do?
The 74×266 gives you four open-collector XNOR gates that can be used individually. An XNOR gate is a logic gate that outputs 1 (HIGH) if its inputs are equal (both 1 or both 0). In the truth table below, you can see what the output will be for any given input:
How To Use This Chip
The 74HC266 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 74HC266 supports 2V to 6V, while the 74LS266 only supports 5V.
Once it’s connected, you can use any of the four open-collector XNOR gates inside.
This chip uses open-collector outputs. That means you can only sink current (current can flow into the chip), not source it (current cannot flow out of the chip).
Each gate output of the 74HC266 can sink about 4 mA when powered with 5V. While the 74LS266 can usually sink about 8 mA of current. These values can vary between manufacturers of the chip though.
How To Use Open-Collector Outputs
The outputs from the 74HC266 are not your normal high/low outputs. Instead, they use something called open-collector. Open-collector outputs are outputs that are connected via a transistor. And the collector of the transistor is available at the pin. For an XNOR gate, it will look like this: