XMEGA A1U Xplained Pro PC2 pulled high?

Go To Last Post
3 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I've noticed that whenever my Xplained pro's PC2 pin is configured as an input, it's reading high? (via PORTC.IN) I've taken a look at the schematics and for my own life I can't see it being pulled high anywhere, and to be fair PC2 is a USART signal so there shouldn't be any need to pull it high anyway. PC0 & PC1 are TWI pins so they are pulled high (this is also causing me problems but I'm just going to remove the two pull ups in that case) and I've checked to see if there's a short between anything there but everything seems fine.

So firstly - am I blind and have missed something in the schematic and PC2 is indeed being pulled high somewhere?

And secondly, has anyone else experienced this? 

 

Edit: Something I forget to mention - I've measured PC2 with a 'scope via pin 13 ox Ext1, and it measures flat 0!? 

Last Edited: Fri. Nov 25, 2016 - 08:30 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Greetings -

 

I wonder how hard that pin is pulled high. It could be hard pull up, as in a logic transistor turned on. Or it could be soft pull up, as in a pull up resistor. Try using a 10K resistor to ground. If it is hard pull up, it will stay close to Vcc. If it drops to around 1V (depending on XMega internal pull up resistors), its soft pull up. 

 

XMega has a much more complex GPIO control structure than Mega, and there may be something that you are just overlooking.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Jim,

 

I'm 99% sure that it's not being pulled up via software (the 1% unsure-ness is whether or not the EDBG is sending some sort of command or something instructing it to enable a pull up). I tested this by disconnecting everything I had connected to the board, erasing the chip, then stepping into the first line of my firmware and observing the IO view from there, and low and behold - PORTC.IN shows PC2 high, with DIR and OUT low, and PIN2CTRL = 0.

The fact that voltage measured on the pin is actually zero, which if you disregard the IN register is what I'd expect going off the other registers, does have me wondering in the back of my mind that perhaps it could be an EDBG and/ or AS7 bug and it's just reporting the status of PC2 in the IN register falsely?