Computer Interfacing
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I don't like it


       Computer Interfacing Forum Index -> I2C bus
Author Message

May 24, 2007 3:30 pm

My comment here would be that if I have ANY other means of communicating with chips - I will always opt for the other way!

I2C is - on the surface - very appealing.

Here we only need two wires to enable bi-directional communications among multiple devices. In the testing business, I have many times needed to implement some sort of I2C interface to my test object - or on my on PCB between chips using this interface.

The problem is the variation among manufacturers as far as their implementation of the protocol.

As the start condition is defined a clock activety while the data line is low - this can very easily result in a "stuch bus" if someone on the bus is holding the data line low all the time. I have seen this - particularly with IC's made by Fujitsu. Generally, the only way to recover from this situation is a reset of the chip involved.

Most IC's will have the option of either I2C or SPI interface. While it does require more lines (4 instead of 2) I'll go with SPI any day of the week.

Another problem with I2C is buffering. You can't just hang some buffer tranceiver chip in the line to increase the line length - as the data line is bi-directionl. The maximum capacitance limitation of I2C results in a max line length of about 3 feet if you are using shielded cable - so this can be a real problem.

The problem comes when one must use a chip made by Philips Semi - as Philips invented the I2C standard - this is usually the only method of communication these chips support.

Philips makes some great chips - especially for video processing - thus, on occasion, I am forced to use I2C.

I have found a very robust device made by a company Calibre, UK - a USB to I2C converter. Works really well in my experience - but it is not cheap.

Sep 20, 2009 2:08 pm

Hi All,

I am a regurarely user of I2C for all kind of units.
Since a quit working, now it is only hobby.
Be there is always succes.
I have a remark on the previous writer Klapa about not beeing able to buffer the bidirectional port.
Philips has a very nice IC for that : 82B715.
It provides biderectional communication for both SDA and SCK, and makes it possible to extend to several meters, without shielding.

Just a remark,



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