Atmega32U4 staying in reset

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

Hey!

I have found a very strange problem on one of my AVR board (own design). AVR type: AtMega32u4, if it matters. Problem is with the RESET pin. I have 10k pullup on the reset line (like one should) but the reset pin is always low. I can program the chip perfectly, read all the fuses change them etc, but when it comes to the actual running of the application it fails.

But when I give the Reset line 5V from a wire with no resistor the application starts, so the code is loaded and is capable of running.

Has anyone encountered this kind of behavior before? Is there a solution to that? Is it maybe a broken AVR?

I have attached the schematic.

Attachment(s): 

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

What is connected to the reset line?

My thinking is this: If you can make it run by applying 5V, then something with a much lower apparent resistance than 10K must be there.

Ar you disconnecting the programmer? Is there ANYTHING else connected?

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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

Nothing connected. Measured the resistance from RESET to GND with the RESET leg disconnected from board and got 300 or 600 ohms (can't remember anymore). Tried everything with and without programmer attached.

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

What happens with a different chip?

I think the reset input has an under voltage protection diode. If it were "blown", the symptoms might be as you describe.That would be a lowish resistance to ground inside the chip.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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

Just soldered on a new chip and this problem is gone. So I somehow managed to blow the protection diode inside the chip? Can You perhaps suggest what could have caused that as I haven't tested the board in any application yet, just sitting on my desk connected to the power supply and ISP. Interesting...

Oh and can this chip be salvaged in any way or is it a total write-off. External protection diode or anything?

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

Hi. I had same problem with this ATTiny2313. I remember I touched NRESET with earthed soldering iron. I do not remember at what voltage GND was then but I am quite sure I violated the specification a bit.
It is still funtional/programmable.

Attachment(s): 

No RSTDISBL, no fun!

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

If that is what happened, the likely cause is a negative voltage capable of delivering well more than 10ma for a good fraction of a second. ESD won't generally do it, but MIGHT when plugging in a programmer.

This is not something that only AVRs are sensitive to. Any CMOS logic is susceptible. And any I/O pin, not just reset.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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

Hmm... Very interesting. I really don't have any negative voltage sources nearby... Could a broken ISP MK2 be a culprit here?

Anyway thanks for the info, I'll keep that in mind next time and be more careful.

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

Note likely bad ISP MK2. It should be a logic-only device with only a single positive supply. Or maybe also an ADC to measure target supply voltage, but still only a single positive supply.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!