[chbot] Interesting presentations at our next meetings ==>I2C problems..

Charles Manning manningc2 at actrix.gen.nz
Sun May 29 22:17:02 BST 2011


Having now completely trampled Richard's original threadOn Saturday 28 May 
2011 13:51:54 Mark Atherton wrote:
> Volker,
>
> Have you tried other AD I2C devices using the
> same master you attempted to read the AD part you referenced ?
>
> What is the mode of failure - no ack ?
>
> Are you sure you have the address correctly set -
> some datasheets place the addr bits shifted from
> the R/W bit so addr 0xA0 could be interpreted as
> a write to 0x50, and 0xA1 could be interpreted as a read from 0x50 etc.
>
> If you want to mail me a device, I have several
> sources of I2C masters and have never had a
> failure with a slave the way that you describe.
>
> -Mark
>
> Re I²C and SPI, I obtained some samples of some pre-production AD
>
> >temperature sensors using those 2 buses, but could not get either to
> >work. The issue seems to be that they are extremely sensitive to signal
> >shape, much more so than other SPI devices I bread-boarded onto an
> >Arduino test platform. These new sensors were absolutely no go with that
> >method.

The reason I2C has more signal integrity issues than SPI is that the I2C wires 
are multi-master and need to be open collector with pull-ups. SPI, OTOH, is 
only single direction so can drive harder.

I would do three things: 
(1) Slow the clocking right down. Start with 10kbits/sec or so. 
(2) Check the pull-ups.
(3) Us short-sh wires (30cm or so max).

> >
> >Does anyone have more info whether my conclusion is correct, and/or what
> >the problem here is eaxctly?
> >
> >Thanks,
> >
> >Volker
>
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