Re: parallel I/O ports & opend darin pins on MPC8xx

Dear Stephan,

in message [ref] 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@denx.de
It is practically impossible to teach good programming style to  stu-
dents that have had prior exposure to BASIC: as potential programmers
they are mentally mutilated beyond hope of regeneration.   - Dijkstra

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/