I2C device identification

phil at netroedge.com phil at netroedge.com
Thu Mar 7 01:37:21 CET 2002


That's a tough question about which is safer or more reliable.  I
guess it depends on the cross-section of devices being probed.  I've
had a mobo a few years ago which would lock up the SMBus (not even the
reset button fixed the condition) if the device at 0x69 was sent a
quick-write.  It turned out to be a clocking chip which hung the bus
because it was anticipating more data following the quick-write and
didn't time out.

Some simple devices only respond to the quick-commands and switch
things on or off depending on it if got a quick-read or write.  In
that case, doing either quick command would cause a potential
state-change in the device instead of doing a non-intrusive probe.

Oh, lastly, I think all I2C/SMBus transations start with a quick-type
transaction.  So, if I have my head screwed on straight, it is
impossible to not detect a chip with a quick-read which supports, say,
a I2C Block-read. 


Phil


On Wed, Mar 06, 2002 at 06:16:55PM -0600, leo.duran at amd.com wrote:
> Phil,
> 
> Thanks for the reply.
> Your observations are in line with what I'm seeing.
> 
> I have a DIMM at 0x50 that's somehow responds to "QuickWrite"
> at 0x30.  But if do a "QuickRead", only the (real) device at
> 0x50 responds.  It's doing a "QuickRead" an OK detection mechanism?
> It seems most people prefer "QuickWrite" for device detection.
> 
> Thanks,
> Leo.
> 
> -----Original Message-----
> From: phil at netroedge.com [mailto:phil at netroedge.com]
> Sent: Wednesday, March 06, 2002 5:59 PM
> To: Duran, Leo; sensors at Stimpy.netroedge.com
> Subject: Re: I2C device identification
> 
> 
> 
> If you see a device at, say, 0x31 and 0x51 which both seem to be
> eeproms, then they are most likely the same device responding to
> either address.  Don't count on most eeproms to show up twice like
> this, though.  It is possible to have devices in the 0x30-0x3f and
> 0x50-0x5f be independant, unqiue devices.  It appears to be rare (at
> least on motherboards). 
> 
> I hope this helps.
> 
> 
> Phil
> 
> On Wed, Mar 06, 2002 at 10:44:15AM -0600, leo.duran at amd.com wrote:
> > Hello,
> > 
> > In the "I2C Tools Page": http://www2.lm-sensors.nu/~lm78/i2ctools.html
> > there is chart listing general devices addresses.
> > 
> > The range 0x30 thru 0x37 is listed as "eeprom shadow", whereas the range
> > 0x50 thru 0x57 is listed as "eeprom".  Does this mean that the same (eeprom)
> > device will respond to both addresses?  Or are these two distint devices?
> > 
> > Thanks for the clarification,
> > Leo Duran.
> > 
> 
> -- 
> Philip Edelbrock -- IS Manager -- Edge Design, Corvallis, OR
>    phil at netroedge.com -- http://www.netroedge.com/~phil
>  PGP F16: 01 D2 FD 01 B5 46 F4 F0  3A 8B 9D 7E 14 7F FB 7A

-- 
Philip Edelbrock -- IS Manager -- Edge Design, Corvallis, OR
   phil at netroedge.com -- http://www.netroedge.com/~phil
 PGP F16: 01 D2 FD 01 B5 46 F4 F0  3A 8B 9D 7E 14 7F FB 7A



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