ATmega128 TWI with internal pullups...

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

Hi,

Has anyone had sucess with using the internal PORTD<1:0> pullups instead of external resistors for TWI on an ATmega128? I have a single external device, close at hand (traces are maybe 2cm & capacitance low) - with 4K7 external pullups, all is fine, with the internal pullups enabled, no joy. 100kHz clock...

Using lastest WinAVR & an ATmega128 dev board from Olimex with Olimex JTAG (nice device!).

I have an ANT8 logic analyser I can play with - I hope that that will shed further light...

Thanks

Nick

Nicko

Last Edited: Wed. Jan 2, 2008 - 09:49 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The internal pull-ups are to weak to work with I2C (TWI).
Maybe if your SCL is verrrry ssssloooow......

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

what size is the internal pullups ?
just wondering :)

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

The numbers that come out of my non-perfect brain memory is 20-50 kOhm

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

Yes, the datasheet for the Tiny25 and Mega168 show 20-50kOhms. Perhaps other AVR parts have different values. The pull-up resistance is listed in the "Electrical Characteristics" section of the datasheet.

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

Okey, new knowledge in the new year :)