Pin Acting Odd

[jmsch...@gmail.com]

Hey all,

I am pretty new to the BBB and I came across something pretty odd that I have been trying to figure out for a few hours now as I was creating a push button circuit:

P9_25 is a GPIO pin.  I set it to input but noticed that it would not respond to my button.  After some digging I realized that the pin itself was acting funky, so I isolated it to run some tests with BB's Bonescript tutorial on GPIO digitalWrite().  I ran this code below (apologies for the sloppy picture) with the adjacent circuit configuration shown as well.  Obviously, the LED should turn off, but it doesn't:

 

I then tried the same tests on other pins, such as P9_26, and it worked perfectly, so that's where I'm startled.

I have two theories:

1)  I messed with P9_25 in the past, and it is reconfigured in a weird way; if someone has this hunch, could you please perhaps inform me how to reset the pin to its original glory?

2) The pin is busted.  Fingers crossed for #1.

If anybody has run into something similar, or has any idea what I should do, please let me know!

Thank you for you time.

-Joe

[Gerald Coley]

Take a look at the schematic. GPIO3_21 is connected to the output of a clock generator. To use it you must disable the Oscillator.

Oscillator can be disabled via SW

for power down modes or if

GPIO3_21 needs to be used

My suggestion is to pick another pin to work with. Less headaches.

Gerald

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Gerald

 

ger...@beagleboard.org

http://beagleboard.org/

[jmsch...@gmail.com]

Okay I think I see what you are saying.  The MODE0 for GPIO3_21 is "mcasp0_ahclkx",  so with that beaglescript code, when I say "b.pinmode("P9_25",b.output)" it is outputting the results of the MODE0 (clock generator output) and not the MODE7(GPIO output) as I had expected?

But if this were the case, in my Python ADAfruit code, I explicitly set that pin to GPIO, so shouldn't behave like that?

Thanks for your help, really trying to get a solid grasp on these concepts!

-Joe

[Gerald Coley]

I can't speak for the SW implementations. I just know how the board was designed.

Gerald

[jmschmitz12]

Okay gotcha. Would you agree with my logic in the first part then (about the beaglescript)?

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[Gerald Coley]

I defer to the creator of BoneScript to answer that. I assume that if the HDMi port were disabled, it frees this pin as well. But maybe not.

Gerald