Re: Strange 8255 behavior

> Michał Pleban wrote:
>
>> It's 2AM now and I am completely of ideas. Does anyone know about what
>> exacly happens in the 8255 when its Control register is written into?
>
> OK, after extensive googling I found this little gem:
>
> http://www.cpcwiki.eu/index.php/8255
>
> "CAUTION: Writing to PIO Control Register (with Bit7 set), automatically
> resets PIO Ports A,B,C to 00h each!"
>
> This information (quite important IMHO) is not found in the datasheet.
> Also, it's a very stupid behaviour for an I/O chip to silently reset the
> port values when the port direction is modified, but it's Intel, so what
> did I expect? :-)
>
> I just have to modify the IPC code logic somehow to work around this...
>
> Regards,
> Michau.
>

What if you write to it without bit7 set?

-Pete