Lecture 13 - Inter-Integrated Circuit (I2C)

Lecture 13 - Inter-Integrated Circuit (I2C)

1. I2C

   • A serial data protocol which operates with a master/slave relationship
     • Any Node can take on the role of Master
   • Uses two wires:
     • Serial Data (SDA)
     • Serial Clock (SCL)
   • Nodes can only pull SDA and SCL down to Logic 0 - but not up to Logic 1
     • Pull-up resistor connected to each line holds then high unless node pulling it low

2. I2C Communications

   • SDA and SCL connected to all nodes
   • Each I2C Node has an assigned address
   • Node initiating data transfer becomes the 'master'
     • Device being addressed is the 'slave'
   • All nodes monitor the bus and responding only to data and commands sent to their own address
   • Data Line (SDA) must be stable when Clock (SCL) is high i.e. Data changes while SCL is LOW
     • SDA High - '1'
     • SDA Low - '0'
   • Each Data Byte followed by an ACK from the receiver
   • Data sent MSB First
   • START signalled by SDA falling while SCL is high
   • STOP signalled by SDA rising while SCL is high

3. I2C ACK Signal

   • The Acknowledgement (ACK) is generated by the receiver after each byte is transmitted to confirm data has been received
   • At the end of each byte (sent by transmitter) receiver acknowledges receipt by pulling SDA Low

4. I2C Addressing

   • The basic I2C System allows a 7-bit address
   • First Byte after START is the address of the device being accessed
   • The 8th bit is the R/W bit
     • 1 = Read
     • 0 = Write

5. I2C Data Transfer

   • Master TX addresses a Slave RX and send 2 bytes of Data
   • Master Reads the Slave immediately after Address Byte

6. I2C on the mbed

   • There are two mbed I2C ports
   • Mbed Master functions and Slave functions
     • Master functions
       • I2C
       • frequency
       • read
       • write
       • start
       • stop
     • Slave functions
       • I2CSlave
       • frequency
       • receive
       • read
       • write
       • address
       • stop

7. I2C Assessment

   • Widely applied to short distance data communication
   • Provides much more reliable systems
   • BUT doesn't not check for errors