Arbitration
Devices can start transmitting at any time
- wait until lines are both high for some minimum time
- multiple devices may start together - clocks will be synchronized
All senders will think they are sending data
- possibly slowed down by receiver (or another sender)
- each sender keeps watching SDA - if ever different (driving high, but its really low) then there is another driver
- sender that detects difference gets off the bus and aborts message
Device priority given to devices with early 0s in their address