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Pull up on D3,D4 on Panda II


#1

Why did you add pullup resistors on these pins? I spent a long time trying to debug this to find out they are pulled up via the schematic. Arduino does not pull up the I2C pins…

Is there a cutable trace to fix this?

If not can make sure you do that in future Revs?


#2

This is a by design and no plans to change it.


#3

So its by design to not have a cutable trace?

I’m not asking for them to be removed.

I’m suggesting that in future revisions you give people an option.


#4

Those pins are open drain and so having a resistor is a must have in most cases (I personally say all). Should you really want it without resistors the you can simply remove the resistors off the board…or cut traces but removing resistors is easier and better. Again, removing the resistors will make the pins nonfunctional as they are open drain.


#5

Michael23,
If you really plan to cut the traces, refer to the eagle files in the documentation.
http://www.ghielectronics.com/downloads/FEZ/Panda_II/FEZ%20Panda%20II%20RevD.zip
It is easy to find. I have no Eagle installed on the system that I am working on now, better I even cannot install it on this system. If you want I could have a look at the board this evening (CET-1) and tell which traces to cut. I agree whit Gus, I think there is really no need to cut these traces.
Cu Wim.


#6

BTW, Open Drain means that the pin can not generate a 3.3V(True) output, it can only produce a 0V(False), or it can float the pin.

The resistor is there for pull the pin to 3.3V of the pin isn’t producing a 0V. This is defined in the I2C spec and is required to be that way.

I can see only 2 reasons to remove the resistor:
[ol]
You already have pull up resistors on your I2C slave
You want to make the pin High Impedance by setting it as an input.
[/ol]

On Panda1 and Panda2 it is R15 and R16…


#7

Cutting tracks is a very definite thing.
Why not just remove resistors R15 and R16.
You can still put them back.
Here is a picture of where the resitors are:
http://www.wimcranen.nl/images/Panda_R15_16.JPG

Cu, Wim.