The 74×164 (ex 74HC164) is a chip that includes an 8-bit serial-in, parallel-out shift register.

Here’s how it works:

• You input data one bit at a time through either of the two serial data inputs (A or B).

• Each time a clock pulse is received, the data shifts along the register.

• Once all bits are entered, you can access the stored data via its 8 parallel outputs (Q0 to Q7).

This chip is great for expanding the number of output lines in a microcontroller project or for serial-to-parallel data conversion.

Why Two Inputs?

The chip has two data input pins, called A and B.

These inputs work together using an AND gate, which means both A and B need to be “on” (or high) for the data to go in. If either A or B is “off” (or low), the data won’t get in.

Having two inputs can be beneficial in some cases:

1. Extra Control: You can control the data better because both inputs need to agree (both high) to let the data in.

2. Reducing Errors: It helps prevent accidental data entry due to electrical noise or spikes making sure both inputs confirm the data.

3. Flexible Setup: You can wire A and B to different signals, allowing more control over when and how data is allowed in.

So, the two inputs give you better handling and flexibility with the data moving into the 74LS164.

How To Use This Chip

The 74HC164 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 74HC164 supports 2V to 6V, while the 74LS164 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 0.8 mA when the pin is high (sourcing) or 16 mA when the pin is low (sinking).

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