I suspect you're exactly right Wulf Man. I was not really paying attention to the order I applied the power and I was assuming that the POT voltage would be isolated from the digital control side of the chip. But I also assumed that if I blew the drivers that I would no longer get any signal from that pin. Is it normal to get a reduced voltage? I suppose I could almost fix the issue with an opamp (except I'd be worried that the defective pin would completely go dark someday.)
If I really did blow those pins then I'll get a good signal out of SPI1 when I test it tonight. How would I prevent this in the future? Maybe some clamping diodes to keep the voltage on the digital pins in range? Walker On Tuesday, March 22, 2016 at 11:09:29 AM UTC-4, Wulf Man wrote: > > Power sequencing is the key. How are you doing this? > If you are applying the 5v to the pots first you may be causing the issue > and blowing the processor pins. > All pins on the processor need to be isolated from everything until power > rails are stable. > Drive a input pin when the processor is not fully powered on and you risk > destroying the drivers in the chip. > > > Schematics of your design would help identify the problem. > > > On 3/22/2016 7:22 AM, Walker Archer wrote: > > Forgot to add info about how the cape is powered. The chip I'm using on > the cape is an AD5206 digital potentiometer (10k). I'm using the 3.3v rail > to power the SPI side and an external 5v (4.9v measured) supply powers the > pots. However, I've been getting voltages from the pots that aren't what > I'd expect, so a few days ago I disconnected the 5v supply and ran the BBB > 3.3v rail to a single pot just to see if the resulting voltages would make > more sense. Maybe that was what did it? > > On Tuesday, March 22, 2016 at 10:15:53 AM UTC-4, Walker Archer wrote: >> >> Thanks for responding Gerald. The scope capture above was done with no >> cape. It was taken from SPI0. The chip has one-way communication so I'm >> only using SPID1 (P9_18 from memory). The clock is coming from P9_22. >> Chip select is P9_17. When I get home tonight I'll try the same from SPI1 >> and see if it's affected as well. >> >> >> >> On Tuesday, March 22, 2016 at 9:39:30 AM UTC-4, Gerald wrote: >>> >>> No way for me to tell what you may have done, but 1.8V is not good. Any >>> chance you can provide more information like the pin number and connector >>> you are using? >>> What do you have connected to this pin? >>> How is that device powered? >>> >>> Gerald >>> >>> >>> On Tue, Mar 22, 2016 at 6:47 AM, Walker Archer <[email protected]> >>> wrote: >>> >>>> I've been building a custom cape for a robotics project and one of the >>>> chips I'm using is controlled via SPI. I've used an oscilloscope to >>>> validate that the SPI is working as expected. However, two days ago I >>>> noticed that the chip stopped responding and after scoping the SPI signal >>>> I >>>> can see that the BBB is sending the SPI data pulses at 1.8v. The SPI >>>> signal is still happening... and the clock signal is still at 3.3v. It's >>>> just the SPI data line that is only peaking at 1.8v. >>>> >>>> So, I'm wondering if I've done something bad to my BBB or if I've >>>> somehow triggered a feature that I don't know about yet. I'm attaching a >>>> photo of the oscilloscope screen that shows the issue. >>>> -- >>>> For more options, visit <http://beagleboard.org/discuss> >>>> http://beagleboard.org/discuss >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "BeagleBoard" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> For more options, visit <https://groups.google.com/d/optout> >>>> https://groups.google.com/d/optout. >>>> >>> >>> >>> >>> -- >>> Gerald >>> >>> [email protected] >>> <http://beagleboard.org/>http://beagleboard.org/ >>> [email protected] >>> >>> -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <javascript:>. > For more options, visit https://groups.google.com/d/optout. > > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
