[TriEmbed] I2C range extension

[John Vaughters]

Charlie,
CAN is by far the most expensive. 485 is cheap (TI chips) but lacks the interrupt capability of CAN and i2c. It really depends on how much you value the interrupt feature. Star confiurations can be made through a communication hub. That is to say a processor with mulitple serial ports. For instance a mega arduino. The purpose of this subsystem would be to handle communications. Therefore you would have multiple serial port networks and each one can be balanced. That is one way to handle a star configuration. It is basically setting up a communications sub-system. It is also a good way to break up other sub-systems of a project, ie legs, arms, sight as examples.
Just to be clear on my description of the interruption feature. This is a feature that allows any device to speak at any time. i2c checks if the bus is busy and will not allow communication if it is busy, but CAN has the most unique feature for handling this problem. Each device has an address and that addressing scheme provides a priority of communication. If multiple devices hit the bus at the same time, the highest priority gets through. It really is a genious idea if you read about it on the electronics level. The bits cancel each other on the bus and the highest priority gets through. It is not quite peer to peer, like a tcp swtich, but it does allow peer interuptions based on priority. The failure would be if you over use the interuptions and the highest priorty is the only communicating device, but this is easily resolved with proper polling and interuptions for emergency situations. 
John Vaughters
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