Serial Buses

Serial Bus Features Allows several devices to be connected to a set of common signal wires Reduces inter-connections and complexity Asynchronous or Synchronous Master - Slave(s) Multiple Masters Standard interfaces and protocols Various bus operation speeds (data rates/ baud rates) various application areas 6-2

Serial data communication Synchronous  use a shared common clock signal.  all devices synchronise with the shared common clock signal.  data transfer occurs on the clock signal – usually a clock transition. Asynchronous  no shared clock  all devices have there own clock  all devices must use the same clock frequency  Tx and Rx clock frequencies may differ slightly between devices  device clock signals are out of phase with each other – not synchronised hence the term asynchronous.  the receiver must synchronise with transmitter in order to receive data correctly. 6-3

Baud Rate In this case: Bit rate = 2 x Baud rate Note: For a binary signal - Baud rate = bit rate = 1/bit time Data Time The baud rate of a data communications system is the number of symbols transferred per second. Bit rate defines the rate at which information flows across a data link. measured in bits/second(bps) For a binary two-level signal, a data rate of one bit per second is equivalent to one Baud T T = The Bit Time The baud unit is named after Jean Maurice Emile Baudot, who was an officer in the French Telegraph Service.

Some common serial buses SPI- Serial Peripheral Interface I 2 C - Inter-Integrated Circuit RS232 - Computer serial port(point to point only) USB - Universal Serial Bus Ethernet - high speed LAN CAN - Control Area network LIN - Local Interconnect Network FlexRay - FlexRay is a fault tolerant bus and provides deterministic data transmission. MOST - Media Oriented Systems Transport MIL-STD-1553 Bus - military avionics & spacecraft 6-5

Applications Chip to Chip connections  SPI and I2C Processing node to peripheral devices  USB  SPI & I2C  LIN Processing node(Computer System) to processing Node  Ethernet  CAN 6-6

Classification of Serial Bus Systems 6-7