I2C Intended Purpose

FirstSteps · Joined: 09 May 2006 Posts: 7

Would any I2C experts comment on this, please?

It is my understanding that I2C was intended only for on-card communication between chips and not intended for off-card networking or over-wire networking.

An example: Wiring up a group of 16 5" x 6" cards with I2C in an area no larger than a desktop, in a high EMI environment.

This would *not* be an appropriate use of I2C. Agreed?

Ttelmah · Guest

A card can 'be' in a high-emi enviroment, but have no great amount of emi present locally, depending (of course) on how well the 'unit' as a whole is shielded. If the connections are in a high-emi location, then I2C, is not the interface of choice, but if there are constraints on the number of connections, most of the 'better' solutions, will require extra wires (differential etc.). However it is possible to improve I2C, for exactly this type of application, but with the need to add extra software/hardware, to ruggedise the connection. You can use active termination, in place of the normal passive pull ups, with overvoltage protection present, possibly opto-coupling, and even perhaps add error checking to the protocol.
Have a look at Philips AN255-02, which describes the use of their PCA9511...PCA9518 'rugged I2C' transceivers. These are designed for 'hot swap' cards in an enviroment, very much as you describe.
So, 'simple I2C', is probably not the interface of choice, but there are I2C extensions, that may make the interface a good choice for the application described. If the system is using such transceivers, then it may be a perfectly good solution.

Best Wishes

kender · Joined: 09 Aug 2004 Posts: 768 Location: Silicon Valley

Originally, the I2C was designed for communication between the smart bettry and the host system. You're right, it was not designed to work in the EMI environment. As Ttelman has mentioned, you could try to ruggedize the I2C. The first thing I woul try is to "simply" shield the inter-board cables.

CAN and RS485 would be a better choice for the EMI environment. On the other hand, the number of peripherals that support CAN is small compared to the number of peripherals that support I2C.