[SI-LIST] Re: I2C Noise
- From: "Chris McGrath" <chris.mcgrath@xxxxxxxx>
- Date: Mon, 24 May 2004 08:32:47 -0700
IIC does not cite a specific pullup value but rather a range of values
that includes 4.7k. We have found that an ideal value depends on the
chips that you use, but 4.7k worked fine for us on some designs.
> -----Original Message-----
> From: k EPD [mailto:epd2001usa@xxxxxxxxxxx]=20
> Sent: Saturday, May 22, 2004 4:31 PM
> To: weirsp@xxxxxxxxxx; Christopher.Jakubiec@xxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: I2C Noise
>=20
>=20
> =20
> I^2 requires a 1.6k pullup , does you circuitry have that? =20
> Also I would
> like to agree with a x-talk problem with other lines , check=20
> you frequency and you coupling to you clock or data line for=20
> the i^2C buss....=20
>=20
>=20
>=20
>=20
> Keith Kowal 781-593-0199 epd2001usa@xxxxxxxxxxx[1] [2] =20
> >From: steve weir
> <weirsp@xxxxxxxxxx> >Reply-To: weirsp@xxxxxxxxxx >To:=20
> Christopher.Jakubiec@xxxxxxx >CC: si-list@xxxxxxxxxxxxx=20
> >Subject: [SI-LIST]
> Re: I2C Noise >Date: Fri, 21 May 2004 16:53:15 -0700 >>Chris,=20
> from your description, it does sound like you are suffering=20
> from >crosstalk. I2C devices are supposed to debounce both=20
> SCL and SDA in the >100KHz mode, and soeven with a lot of=20
> crosstalk, you should not have seen >errors. Unfortunately,=20
> there is a lot of silicon that violates the spec. >Regards,
> >>>Steve >At 03:24 PM 5/21/2004 -0700, Christopher Jakubiec wrote:=20
> >>>>>Steve,
> >>>>Thanks for your insight. Yes, I meant to state 100kHz instead of=20
> >>>>100mHz. I think that we might be dealing with item 2 (noise=20
> >>>>>>coupling) as you
> described below. We have 3 AC/DC power supplies that each=20
> >>operate on dual power grids for redundancy purposes. Each=20
> power supply has 2 >>sets of I2C wires connected to it, one=20
> for each power grid. I believe >>that each >>set consists of=20
> SCL, SDA, VDD, VSS. At one point in the system all 6 sets=20
> >>of I2C >>wires are bundled together. >>>>On a system that=20
> was failing fairly consistently, we >>went in and seperated=20
> the cumulative bundle into individual sets by >>physical=20
> distance. >>We have not seen the failure replicate since. I=20
> don't believe that the >>orginal wire >>routing included any=20
> special shielding. I can confirm with a digital >>scope per your
> >>suggestion. >>>>-Chris >>>>>>steve weir wrote: >>>>>>Chris,=20
> >>>>>>I2C=20
> >>is a
> very high impedance bus, typically 4700 ohms pull-up. I think=20
> you >>>mean 100Kbps, the legacy mode. It is easy to mess I2C=20
> up with grounding
> >>>issues.The states tha t you are referring to are probably being=20
> >>>conveyed via IPMB over I2C or similar. There are several=20
> things that=20
> >>>can go wrong:
> >>>>>>1) Incorrect grounding is fouling basic I2C signaling.=20
> >>>2) Noise
> coupling is fouling I2C signaling. >>>3) Voltage translation=20
> issues. The original I2C bus was 5V TTL. Mixed >>>voltages=20
> can also cause grief, as can hot swap. >>>>>>Check 1 and 2=20
> with any of the many I2C analyzers available, or just put a=20
> >>>scope on the SCL line in infinite persistance. >>>>>>4) An=20
> aberrant device is violating I2C bus negotiation contending with the
> >>>actual master and fouling SCL, SDA or both.. >>>>>>5) Your=20
> >>>misbehaving
> peripheral is a poor implementation of I2C and/or >>>whatever=20
> protocol you may be running on top of it. Some devices do not=20
> >>>implement the timing as per the spec. This can be=20
> particularly true of >>>microcontrollers that do not include=20
> dedicated I2C hardware. But even a >>>number that do violate=20
> the specs, or rely on careful programming to comply. >>>>>>I=20
> would start by looking at the SCL line with a decent digital=20
> scope >>>first. If you don't find your problem there it is=20
> time to look for mixed >>>voltage and/or hot-swap issues. If=20
> you get all that worked out, then I >>>would move up to the=20
> link layer and see if you are a victim of some bad >>>firmware.
> >>>>>>Regards, >>>>>>Steve >>>>>>At 02:04 PM 5/21/2004 -0700,=20
> >>>>>>Christopher
> Jakubiec wrote: >>>>All, >>>>>>>>Has anyone encountered=20
> problems with EMI/noise issues on I2C wires and/or=20
> >>>>busses? We use industry standard I2Cto interface with our=20
> bul k 208V/48V >>>>AC/DC power supplies. We are observing=20
> instances where control and status >>>>signals (connected via=20
> I2C) for the AC/DC power supplies appear to be=20
> >>>>intermittently >>>>in the wrongstate. I believe that we=20
> are currently running the I2C clock >>>>signal at >>>>100MHz,=20
> and our wire lengths are significant on the order of 2-3ft.
> >>>>>>>>Thanks, >>>>>>>>Chris Jakubiec >>>>Sun Microsystems
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