Registers

A register is a small piece of memory in a digital device. Each register is generally used to control settings and behaviours of the device. Most registers are 8 bits, but some can be 16 bits, 24 bits, or more.

For the 32M1, you write to its registers directly using built-in AVR constants. For SPI devices, you can read and write register values by sending specific SPI messages as described in the component’s datasheet. Descriptions of registers are generally one of the most important things to look for in a component’s datasheet.