Re: Strange 8255 behavior

From: Michał Pleban <*lists_at_michau.name*> Date: Sun, 10 Jun 2018 19:02:40 +0200 Message-ID: <5B1D59B0.50604@michau.name> · lists_at_michau.name

smf wrote:

> It's mentioned in here
> http://pdf.datasheet.live/19afa754/intel.com/P8255A.pdf
> "All of the output registers, including the status flip-flops, will be
> reset whenever the mode changes."

Hm, how did I miss that?

But it's not true anyway. The registers are reset on only when *mode8
changes, but also when *direction* changes, or even when *nothing*
changes. I.e., even if you write the control register with the same
value that was written before, the registers are still reset. That's not
what the datasheet says.

> I withdraw my earlier comment.. Why can't you use"mode 2 -
> bi-directional bus"?

Same as with the AM2130 - I want to maintain software compatibility with
the original card on the 6509 side.

Regards,
Michau