The Serial Peripheral Interface Bus is a synchronous serial data link standard that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select (chip select) lines.
The SPI bus specifies four logic signals:
- SCLK: Serial Clock (output from master);
- MOSI; SIMO: Master Output, Slave Input (output from master);
- MISO; SOMI: Master Input, Slave Output (output from slave);
- SS: Slave Select (active low, output from master).
Operation
The SPI bus can operate with a single master device and with one or more slave devices.If a single slave device is used, the SS pin may be fixed to logic low if the slave permits it. Some slaves require the falling edge (high?low transition) of the slave select to initiate an action such as the Maxim MAX1242 ADC, which starts conversion on said transition. With multiple slave devices, an independent SS signal is required from the master for each slave device.
