What is I2C? How does it work? // Technology

High speed mode

When working with high speed mode devices the protocol changes slightly.

The address frame extends out to include a master code which is transmitted at normal I2C clock rates but then starts clocking data at a faster rate for the rest of the interaction.
Any device capable of high speed mode will recognize this special master code and drop into high speed mode for the duration of the interaction.

Once complete all devices drop back down to normal clock rates.

Ultra Fast Mode

With the 5MHz Ultra Fast Mode things change even further.

  • The SCL and SDA lines are used in a similar way to USB and ethernet lines.
  • It’s a uni-directional protocol, so slaves don’t send any ACK response and there’s no multi-master capability.
  • There’s also only 112 addresses available.
  • So, UFM is used for write only devices, such as LED strips and displays.