[SI-LIST] Re: I2C Noise

 
I^2 requires a 1.6k pullup , does you circuitry have that?     Also I would
like to agree with a x-talk problem with other lines , check you frequency
and you coupling to you clock or data line for the i^2C buss.... 




Keith Kowal 781-593-0199 epd2001usa@xxxxxxxxxxx[1] [2]   >From: steve weir
<weirsp@xxxxxxxxxx> >Reply-To: weirsp@xxxxxxxxxx >To:
Christopher.Jakubiec@xxxxxxx >CC: si-list@xxxxxxxxxxxxx >Subject: [SI-LIST]
Re: I2C Noise >Date: Fri, 21 May 2004 16:53:15 -0700 >>Chris, from your
description, it does sound like you are suffering from >crosstalk. I2C
devices are supposed to debounce both SCL and SDA in the >100KHz mode, and
soeven with a lot of crosstalk, you should not have seen >errors.
Unfortunately, there is a lot of silicon that violates the spec. >Regards,
>>>Steve >At 03:24 PM 5/21/2004 -0700, Christopher Jakubiec wrote: >>Steve,
>>>>Thanks for your insight. Yes, I meant to state 100kHz instead of 100mHz.
>>>>I think that we might be dealing with item 2 (noise >>coupling) as you
described below. We have 3 AC/DC power supplies that each >>operate on dual
power grids for redundancy purposes. Each power supply has 2 >>sets of I2C
wires connected to it, one for each power grid. I believe >>that each >>set
consists of SCL, SDA, VDD, VSS. At one point in the system all 6 sets >>of
I2C >>wires are bundled together. >>>>On a system that was failing fairly
consistently, we >>went in and seperated the cumulative bundle into
individual sets by >>physical distance. >>We have not seen the failure
replicate since. I don't believe that the >>orginal wire >>routing included
any special shielding. I can confirm with a digital >>scope per your
>>suggestion. >>>>-Chris >>>>>>steve weir wrote: >>>>>>Chris, >>>>>>I2C is a
very high impedance bus, typically 4700 ohms pull-up. I think you >>>mean
100Kbps, the legacy mode. It is easy to mess I2C up with grounding
>>>issues.The states tha t you are referring to are probably being conveyed
>>>via IPMB over I2C or similar. There are several things that can go wrong:
>>>>>>1) Incorrect grounding is fouling basic I2C signaling. >>>2) Noise
coupling is fouling I2C signaling. >>>3) Voltage translation issues. The
original I2C bus was 5V TTL. Mixed >>>voltages can also cause grief, as can
hot swap. >>>>>>Check 1 and 2 with any of the many I2C analyzers available,
or just put a >>>scope on the SCL line in infinite persistance. >>>>>>4) An
aberrant device is violating I2C bus negotiation contending with the
>>>actual master and fouling SCL, SDA or both.. >>>>>>5) Your misbehaving
peripheral is a poor implementation of I2C and/or >>>whatever protocol you
may be running on top of it. Some devices do not >>>implement the timing as
per the spec. This can be particularly true of >>>microcontrollers that do
not include dedicated I2C hardware. But even a >>>number that do violate the
specs, or rely on careful programming to comply. >>>>>>I would start by
looking at the SCL line with a decent digital scope >>>first. If you don't
find your problem there it is time to look for mixed >>>voltage and/or
hot-swap issues. If you get all that worked out, then I >>>would move up to
the link layer and see if you are a victim of some bad >>>firmware.
>>>>>>Regards, >>>>>>Steve >>>>>>At 02:04 PM 5/21/2004 -0700, Christopher
Jakubiec wrote: >>>>All, >>>>>>>>Has anyone encountered problems with
EMI/noise issues on I2C wires and/or >>>>busses? We use industry standard
I2Cto interface with our bul k 208V/48V >>>>AC/DC power supplies. We are
observing instances where control and status >>>>signals (connected via I2C)
for the AC/DC power supplies appear to be >>>>intermittently >>>>in the
wrongstate. I believe that we are currently running the I2C clock >>>>signal
at >>>>100MHz, and our wire lengths are significant on the order of 2-3ft.
>>>>>>>>Thanks, >>>>>>>>Chris Jakubiec >>>>Sun Microsystems
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