SPI Architecture

SPI uses master/slave architecture and requires four logic signals. The "master" is usually the microcontroller, which reads and writes the multiple slave devices, which are the sensors or actuators. The four lines are as follows:

1. SCLK - Serial Clock, which is output from the master and syncs all the devices
   
2. MOSI - Master Out Slave In, which is data output from the master
3. MISO - Master In Slave Out, which is data output from the slave device
4. SS - Slave Select, which switches which device the master is talking to at a given time