How to drive 595 shift registers with AVR hardware SPI

A pair of shift registers connected with jumper wires on a breadboard

Driving a shift register using an AVR chip’s built-in hardware is really quite easy. Most of their offerings have an SPI module, or Serial Peripheral Interface. A shift register is exactly that, a peripheral device that communicates via a serial line. All we need to do is hook up our connections and use a few pieces of simple code. Join me after the break to see how that’s done.

Just want to know how shift registers work? Check in on my other post on that topic.

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How Shift Registers Work

Shift Registers are integrated circuits that take a serial input and turn it into a parallel output. This is extremely valuable if you need more input/output pins than your microcontroller has available. For hobbyists the most common use is driving LEDs with a 595 shift register. Let’s look at how this is done.

After the jump I’ll discuss control methods, and I’ve assembled a video that illustrates the functions of a shift register.

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