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

Components

The gumstix processor....

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