MOSI
- Master Data Output, Slave Data Input
MISO
- Master data input, Slave data output
SCLK
- Clock signal, generated by the master device, up to fPCLK/2, slave mode frequency up to fCPU/2
SS/CSS
- Slave enabled signal, controlled by the master device, some ICs will be labelled as CS (Chip select)
SDA
- Serial Data Line
- Transmit communication data
SCL
- Serial Clock Line
- Transmit CLK signals, generally provided by the master device to the slave device