SPI: Electrical


There is no special electrical requirement
But according to you working speed you need to care about
Capacitive coupling
Bounces

Usually transmission happens at 0/3.3V, but it is variable
Like what happens with I2C, you must agree with the peripheral
Most peripherals nowadays are 2.7-3.6V or 1.7-3.6V

4 modes or operation are supported:
CPOL (clock polarity) can be either one
CPHA (clock phase) can be either one
This is a serious problem when you connect more than 1 device

Fortunately, SSEL is always active low
But sometimes you must pulse it high among words
And sometimes you must keep it low for the whole transaction
And always is not really always