Difference between revisions of "I2C"
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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. | 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 == | == Task List == | ||
Revision as of 06:08, 14 June 2007
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
- Basic I2C working from Gumstix (completed)
- VFAT powered on and responding to I2C
- I2C controlled from a C program on Gumstix
- I2C transmission line testing
- 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