Re: SPI troubles

[Ned Forrester <nforrester-/d+BM93fTQY@public.gmane.org>]

On 03/14/2010 10:44 PM, Ben Gamari wrote:
> 
> When measuring the SIMO signal on the expansion connector with my daughterboard
> connected, I noticed that the daughterboard's level shifter appeared to be
> driving the signal higher than it should, to ~2.9 Volts. I then checked the
> 1.8V rail voltage and found that it too was higher than expected, again at 2.9
> volts. When I unplug the daughterboard, the 1.8V rail voltage returns to its
> expected value.
> 
> I'm both perplexed and concerned with this behavior. I completely fail to
> see how my board is raising the voltage on the 1.8V rail (schematic available
> at [3]).  While the BeagleBoard seems quite stable, I'm very concerned that
> perhaps the daughterboard over-drove the SIMO ball and burned out some subset
> of the OMAP.  Regardless, as mentioned earlier, I have verified the
> functionality of the same ball as a GPIO input. Thus, I am thoroughly confused.
> Is it possible that the ball's GPIO receiver could remain functional while the
> McSPI receiver is burned out?
>
> [3] http://goldnerlab.physics.umass.edu/git?p=tracker-board.git;a=summary

I'd be happy to check your circuit for you, if it were posted in a more
widely used format.  How about a PDF of the schematic.

-- 
Ned Forrester                                       nforrester-/d+BM93fTQY@public.gmane.org
Oceanographic Systems Lab                                  508-289-2226
Applied Ocean Physics and Engineering Dept.
Woods Hole Oceanographic Institution          Woods Hole, MA 02543, USA
http://www.whoi.edu/
http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212
http://www.whoi.edu/hpb/Site.do?id=1532
http://www.whoi.edu/page.do?pid=10079


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