Re: [Gumstix-users] robostix and gpsstix I2C

[Dave H. <dhy...@gm...>]

Hi Jon,

On 6/20/06, Jon Keller <jo...@65...> wrote:
> I rewired it all following the instructions below, I wired to the bottom
> of the headers pins, the sda and scl headers both had grounds right next
> to each so I used those. Still seem to be getting the same error though.
>
> Are each of these pins bi-directional? On the board they are labeled tx
> and rx. If they weren't bi-directional would adding the 20k resister to
> an already 3.3v coming from the gpsstix drop it even more? Maybe I'm way
> off, but I still get the "gumstix user.warn kernel: i2c: error:
> exhausted retries" error.

Yes, both pins are bidirectional. The Tx and Rx pins are misnomers.

Pin 12 is SDA, and pin 16 is SCL. They're both 5v logic levels and
have 10k pullups to +5.

The problem is that the gumstix can only tolerate 3.3v, so my idea was
to add the 20k to get the pullups to drop to 3.3v.

Did you connect the grounds up between the robostix and the gpsstix?

You should measure 3,3v on the robostix SDA and SCL lines with the 20k
resistors in place.

I'll see if I can get something working here....

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/