Re: Strange 8255 behavior

On Sun, Jun 10, 2018 at 04:59:52PM +0200, groepaz@gmx.net wrote:
> Am Sonntag, 10. Juni 2018, 16:52:24 CEST schrieb Segher Boessenkool:
> > On Sun, Jun 10, 2018 at 04:41:41PM +0200, groepaz@gmx.net wrote:
> > > Am Sonntag, 10. Juni 2018, 16:38:24 CEST schrieb Segher Boessenkool:
> > > > On Sun, Jun 10, 2018 at 04:06:21PM +0200, groepaz@gmx.net wrote:
> > > > > Am Sonntag, 10. Juni 2018, 15:55:10 CEST schrieb Segher Boessenkool:
> > > > > > On Sun, Jun 10, 2018 at 03:39:42PM +0200, groepaz@gmx.net wrote:
> > > > > > > if its similar as with what ppl did with 6522 and 6526 (i would
> > > > > > > assume
> > > > > > > it
> > > > > > > is) - then expect every dirty trick you can imagine being used by
> > > > > > > real
> > > > > > > world software. for example even the subtle differences between
> > > > > > > the
> > > > > > > port
> > > > > > > drivers of port 1 and port 2 are relevant in 6522/26 emulation.
> > > > > > 
> > > > > > (Is there any difference on the 6526?)
> > > > > 
> > > > > yes, unfortunately its not documented in detail anywhere (like in the
> > > > > 6522
> > > > > datasheet) - but experimentation shows that very likely the port
> > > > > drivers
> > > > > have the exact same differences/properties:
> > > > > 
> > > > > the obligatory test program is here:
> > > > > 
> > > > > https://sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/CIA/ciapor
> > > > > ts/
> > > > 
> > > > The datasheet for the 6526 shows PA and PB with exactly the same source
> > > > current (and other electrical characteristics).
> > > > 
> > > > Looking at the actual silicon die I didn't notice any difference either,
> > > > hrm.  Maybe I missed something.
> > > > 
> > > > Or those test programs are seeing the effect of the keyboard circuitry?
> > > 
> > > there is no "circuitry" in the keyboard, other than wires and switches :)
> > 
> > Yes, so a lot of resistance and capacitance :-)
> 
> sure, but the exact same thing connecting different ports makes a 
> difference... if the the ports would be exactly alike, it wouldnt matter :)

http://siliconpr0n.org/map/mos/6526/mz_mit20x/

The ports are the low half of the pins (PA on the left, PB on the right).

(I have a .xcf if anyone is interested, marked quite a few signals, but
I haven't done the port stuff very much.  It's about 400MB).


Segher