[A83] Re: in/out

To: assembly-83@lists.ticalc.org
Subject: [A83] Re: in/out
From: Peter-Martijn Kuipers <hyper@hbyte.net>
Date: Thu, 21 Mar 2002 18:26:08 +0100 (CET)
In-Reply-To: <000601c1d0d0$cfcbcee0$d905040a@kotnet.org>
Reply-To: assembly-83@lists.ticalc.org


On Thu, 21 Mar 2002, Tijl Coosemans wrote:

> > From: "Patai Gergely" <patai.ti@freemail.hu>
> >
> > I'm just reading this:
> >
> > When direct addressing is used (in a,(n); out (n),a) the
> > address n is output on the lower 8 address lines, while the
> > contents of a appear on the higher 8 address lines.
> >
> > Contrary to this, in the case of indirect addressing (in r,
> > (c); out (c),r) the data in the register given appears on
> > the data lines, while the contents of _BC_ are output on
> > the address lines, i. e. 65536 ports can be addressed.
> >
> > Is that true?
> 
> B appears on the top half of the address bus as a side effect of the
> internal structure. The IO device only gets selected with the lower part of
> the address bus.
> 
> At least that's what the official docs say.

Nevertheless, it appearently means you can wire a z80 processor to work
with 65536 ports this way. It would ofcourse be useless, since it's
already hard to fill up the 255 ports :-)

References:

[A83] Re: in/out

From: "Tijl Coosemans" <tijl@ulyssis.org>