Re: [Gumstix-users] [DuoVero] External pull-up for HDQ_SIO line on Crystal COM boardl?

[Ash C. <as...@gu...>]

Hi Philipp,

Short answer: there is a 10K pull-up to 1.8V internal to the DuoVero
COM on the HDQ_SIO line.

Longer answer: I agree---this is an error in the design (my error in
fact for which I sincerely apologize).  I've logged this as a bug
internally as something we should wrestle with for the next revision.
If you are comfortable with a soldering iron and need to pull these
off, I can provide the location of the resistors on the current
revision of the COM.  I reviewed the schematic for the DuoVero COM
this morning and I don't see any supplemental pull-ups on lines that
are broken out.

--Ash

On Tue, Sep 17, 2013 at 1:56 AM, Philipp Lutz <phi...@dl...> wrote:
> Hi,
>
> I'm working with the Parlor/Crystal combo and wanted to change the
> default pinmuxing to have some GPIOs available on the 40pin header. For
> my application it turned out that the signal HDQ_SIO / GPIO127 would be
> convenient to use.
> However I always wondered why the signal is driven high as soon as I
> changed the pinmuxing and changed the direction to input. When I
> activate the build-in pull-down via PADCONF registers, I see a voltage
> of around 1V, so it seems there must be one resistor driving the pin to
> VCC. In the parlor schematics I didn't find any pull-up, the signal
> coming from the gumstix high-density connectors seems to be directly
> routed to the 40pin header.
> So again this pull-up is supposed to be on the COM board which I really
> don't like (to say the least). We already figured that out for I2C2 and
> I2C3, see
> http://gumstix.8.x6.nabble.com/I2C-pull-ups-on-the-DuoVero-td4967758.html
> I don't understand why one would do peripheral related things like that
> on a COM board, this renders I2C2, I2C3 and the HDQ interface useless
> for other pinmuxing modes, even for custom peripheral boards....
>
> @Ash: Are there even more of these build-in pull-ups on the crystal COM
> board?
>
> Cheers
> Phil
>