XMEAG32A4 I/O pin's slow rise and fall transition

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

I just started using XMEGA32A4. Used to use other AVRs. Anyway, after tested it with simple I/O on/off code, found that I/O pin's rise and fall are very slow, compared to other AVRs. Is it normal? For example, Mega2560 can drive I/O pin at 1MHz with minimal rise and fall time while XMega's I/O pin shows almost saw-teeth waveform at 30KHz. The output's interal drive circuit is configured as totempole and no srew rate limit.

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

What is the load on the pin?

Leon Heller G1HSM

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

Hi, Thank you for your response. Right now, I just have a scope's probe, that's all. I also tried another chip just in case the previous may have been broken, but the same result.

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

Hi, Here is the update. I was only testing PORTA0, but tried another port PORTA1..7, and found that they can run very fast. I am using STK600 right now and it is obvious that some capacitance is hanging on trace between the chip and PORTA0 pin on STK600. Need to look into the STK600's schematic and contact Atmel if I can't find anything in the schematic. I used the same pin on the board when tested Mega2560, so it could be something on the routing board. Thank you very much for paying attention to this. Thank you.

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

I got the response from ATMEL about STK600 board design, and found that there is the cap on PORTA0 of the routing card. It is for the same pin being used as AREF.

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

Although that particular pin appears to have a cap on it, note that each I/O pin on the Xmegas have individually controlable slew rate limiting.

A Manual, Section 13.10 Slew-rate Control.

JC

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

Yes, I am aware of it and thank you.

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

DocJC wrote:

A Manual, Section 13.10 Slew-rate Control.

I`ve read this section. The most useful info of this section is " For information about the characteristics of the slew-rate limiter, please refer to the device data sheet."
Ok, searching for "slew-rate characteristics" in pdf 8068T–AVR–12/10,"8/16-bit XMEGA A3 Microcontroller. ATxmega256A3 ATxmega192A3 ATxmega128A3 ATxmega64A3" (using xmega256a3).
Ctrl+F, "slew-rate". There`s only one place, explaining the "slew-rate characteristics" - Section 20.1."TWI - Two Wire Interface. Features". Not good :)

The point is to understand, how to configure external interrupt for fastest technological process stop. The CPU reaction must be of maximal speed.
What am I doing wrong? :)
All I`ve done is "copypast" of the example code of the port-driver example (example port&pin and device`s "fast input" are all the same :o)
Where can I find the detailed slew-rate explanations?

Thank you.

ps: sorry for my poor english.

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

I asked about slew rate value from atmel support and I'll tell the result in a new topic asap.

Ozhan KD
Knowledge is POWER