Am 22.03.2022 um 09:50 schrieb Andy Shevchenko:
On Tue, Mar 22, 2022 at 10:39 AM Hans Kurscheidt <lve0200@xxxxxxxxx> wrote:
Am 22.03.2022 um 09:36 schrieb Hans Kurscheidt:
Am 22.03.2022 um 01:59 schrieb Kent Gibson:
...
Still 1 more question. I understand the sense of a Pull-up in Input
mode, but reading the code, I see that the Bias option exists as well
for gpioset (Output). What is the sense of this, and what does it do?
I guess we started providing OPEN SOURCE / DRAIN in libgpiod v2.0
(Bart or Kent may correct me), but you should get an idea why it may
be useful.
On top of that, the pin can be reconfigured from input to output and
vice versa at run-time. So, keeping a bias setting will allow not to
think about it when pin direction is switched, although I agree this
may not be a clean case to use.
Hi Andy,
Open Source/Drain is completely different from Pull_UP/DOWN! Open
source/drain defines, which active element (transistor) is attached to
the line, while pull_up/down defines, which passive element (resistor)
is attached to the line. In some sense one could say, what pull_up/down
is for input, open drain/source is the corresponding thing for output,
but they are realized by different means. IMHO, "bias" (pull-up/down)
should be an option for gpioget, while "drive" makes only sense for
gpioset, because I understand them as mutually excluding, but may be,
I'm overseeing something.
Unfortunately, this leads me to yet another question: Bias defines
"as-is" and "pull-up/down" as options. Just to be sure, that would imply
that one has to set the bias option to pull_up/down for the first call
to gpioget and that subsequent readings from the input pin should/can
run w/out the bias option, hence "as-is", or do you recommend to have
the bias option specified for each read from the pin?
