Re: Strange 8255 behavior

From: Segher Boessenkool <segher_at_kernel.crashing.org>
Date: Sun, 10 Jun 2018 09:52:24 -0500
Message-ID: <20180610145224.GD27520@gate.crashing.org>
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/ciaports/
> > 
> > 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 :-)


Segher
Received on 2018-06-10 17:02:52

Archive generated by hypermail 2.2.0.