Hello,
I wrote:
has anybody of you experienced problems with accesses to port data
registers on a MPC8255 yet?
...
quoted hunk
- writing port A data register (as 32 bit word) and then looping
reading it back will show that it takes some time for the write to
take effect, i. e. we can read the old value for some time and
then, bit for bit, the new value becomes visible.
Problem solved. The solution was simple. Looking closer I found that
the effect showed only up for bits changing from 0 to 1. Then I saw
that ports pins in question are configured as open drain. When
switching a pin to 1 the level would rise slow enough that reading
the data register would pick up a low (0) for several cycles.
So actually it was no problem at all, just some slow circuitry and a
fast CPU. Don't know why the MPC8260 behaves differently (internal
pull-ups?).
Wolfgang Denk
--
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd@denx.de
The human mind ordinarily operates at only ten percent of its capaci-
ty - the rest is overhead for the operating system.
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