I2C

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 ?0 to ?F where ? is determined by the sum of the addressing bits (ie green & orange high is an address range of 30-3F). For development we'll assume blue high, orange and green low for a range of 40-4F

Task List

1. Basic I2C working from Gumstix (completed)
2. VFAT powered on and responding to I2C (completed)
3. VFAT read/write sqecific registers
4. I2C controlled from a C program on Gumstix
5. I2C transmission line testing
6. 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