SPI (Serial Peripheral Interface) Communication

SCLK – Serial Clock (that is an output of the master)

MOSI  – Master Output; Slave Input

MISO  -  Master Output; Slave Input

SS       – Slave Select (active low)

How SPI communication happens

• Master should configure a clock that the slave device supports. (Typically the frequency range is from 1-100MHz)
• Master should transmit the appropriate CS signal to the slave device.
• A full duplex transmission can be supported since separate lines for maser input and output are available.
• Depending on the application we can decide on the method that we want to use in our application (full duplex or half duplex).
• When data transmission happens, SPI clock should be available. Otherwise data transmission will not happen properly. When no data is transmitted clock should be stopped.

Clock polarity and phase

When clock polarity is zero

  Clock phase is zero

      Data are read at the rising edge of the clock and data are written at the falling edge of the clock
  Clock phase is one

      Data are read at the falling edge of the clock and data are written at the falling edge of the clock.

When clock polarity is one
   Clock phase is zero
      Data are read at the falling edge of the clock and the data are written at the rising edge of the clock.
   Clock phase is one
      Data are read at the rising edge of the clock and the data are written at the falling edge of the clock.

When data transmission happens, normally MSB is put to the data line first.(shown in the above figure)

Note : Figures are take from Wikipedia

Reference: Wikipedia article on Serial Peripheral Interface Bus

        http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus  [Accessed date: 30-06-2012]