Serial Peripheral Interface (SPI)

• serial

• full-duplex

• master-slave (one master, multiple slaves)

• 4 wires:

  • SCLK: Serial Clock (output from master)
  • MOSI: Master Out Slave In (data output from master)
  • MISO: Master In Slave Out (data output from slave)
  • CS /SS: Chip/Slave Select (often active-low, output from master to activate communication on device)

• Clock frequency: typically few MHz

• Word size usually 8 bit

• Topology:

  • independent slaves (parallel)
  • daisy chain

• Throughput:

  • depending on clock speed and electrical characteristics of the connecting wires
  • up to 60 Mbps (in some cases, over short distances)
  • usually less than 10 Mbps

• Pros/Cons:

  • Pro:
    • Full duplex communication
    • Higher throughput than I2C
    • Slaves don’t need own clock oscillator
    • No unique addresses needed
  • Cons:
    • More pins/wires than I2C
    • No control flow, acknowledge of received messages and error checking
    • Only for relative short distances (compared to RS-232, RS-485, or CAN-bus)
    • variations between vendors can lead to difficulties

• Uses:

  • temperature and pressure sensors, touchscreen, LCD
  • ADC/DAC, digital potentiometers
  • Communications devices: Ethernet, WiFi, USB, UART, CAN, ZigBee
  • flash and EEPROM
  • Real-time clocks
  • SD and MMC cards

I2C (Inter-Integrated Circuit)

• serial

• half-duplex

• SMBus is a subset of I2C.

• 2 wires:

  • data (SDA)
  • clock (SCL)

• 10 bit addresses

• Bitrate:

  • 0.1-5.0 Mbit/s