parallel I/O ports & opend darin pins on MPC8xx

[Wolfgang Denk]

Dear Stephan,

in message <FCEAKDJJAPHPLJFINDAJOEFEDEAA.Stephan.Linke at epygi.de> you wrote:
>
> on one of our boards we are using one of the I/O pins in open drain mode. This leads to some problems in combination with other

Please don't use such long lines, they are hard to read.

> drivers that write to the ports data register. Since they can not detect the current output value of the open drain pin. They only
> see the status of the I/O pin no matter who forces the value the CPM or another device connected to the open drain pin. After
> writing back the value read from the I/O data register this value is forced by CPM which is normaly wrong.

This is a feature. It allows you to detect the the state of  the  pin
which can be pretty useful.

> Did anyone run into that problem in the past? What was your solution? Any thing else but NOT using open drain pins?

It is _not_ a problem, it is a feature, and a useful one.

Solution? What is so difficult about latching your output value in  a
variable?


Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
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