Serial Peripheral Interface Bus - Interface

Interface

The SPI bus specifies four logic signals:

• SCLK: serial clock (output from master);
• MOSI: master output, slave input (output from master);
• MISO: master input, slave output (output from slave);
• SS: slave select (active low, output from master).

Alternative naming conventions are also widely used:

• SCLK: SCK, CLK: serial clock (output from master)
• MOSI: SIMO, SDI, DI, DIN, SI, MTSR: serial data in; data in, serial in, master transmit slave receive
• MISO: SOMI, SDO, DO, DOUT, SO, MRST: serial data out; data out, serial out, master receive slave transmit
• SS: nCS, CS, CSB, CSN, nSS, STE: chip select, slave transmit enable (active low, output from master)

The SDI/SDO (DI/DO, SI/SO) convention requires that SDO on the master be connected to SDI on the slave, and vice-versa. Chip select polarity is rarely active high, although some notations (such as SS or CS instead of nSS or nCS) suggest otherwise.

SPI port pin names for particular IC products may differ from those depicted in these illustrations.