I2C

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Parameters for the operation of the VFAT board are downloaded to the chip using the I2C protocol.
A good overview of I2C is available on wikipedia

Electrical Characteristics

The I2C specification limits the I2C bus capacitance to 400pF. The cat5e wire specification limits wire capacitance to 50pF/m, so we should be able to push I2C at least 8m. Testing is needed, but by lowering the bus clock and the pull-up resistors a much greater length should be possible.

VFAT I2C Addressing

With the test rig the addressing wires are as follows:

  • Wh/Green - Least Significant Bit (1)
  • Wh/Orange - Middle Bit (2)
  • Wh/Blue - Most Significant Bit (4)

Oddly (compared to most I2C devices) the VFAT appears to respond to a range of 16 addresses. These addresses are in the range 0x?0 to 0x?F where ? is determined by the sum of the addressing bits (ie green & orange high is an address range of 30-3F).

Task List

  1. Basic I2C working from Gumstix (completed)
  2. VFAT powered on and responding to I2C
  3. I2C controlled from a C program on Gumstix
  4. I2C transmission line testing
  5. Interface Gumstix to controller computer (sockets/web?)

Stuff to buy

  • Power Supply
  • Gumstix (x2)
    • Motherboard
    • Network card
    • Breakout Board
    • Power Plug
    • CF Card
  • I2C expanders
  • I2C eproms (for feedback testing)
  • header pins
  • header pin connectors
  • LED's