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Message from discussion RFC: ULA Replacement for ZX Spectrum SE
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Andrew Owen  
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 More options May 18 2000, 3:00 am
Newsgroups: comp.sys.sinclair
From: Andrew Owen <ao...@brandnewco.org>
Date: 2000/05/18
Subject: Re: RFC: ULA Replacement for ZX Spectrum SE
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in article 392381B0.1B881...@interchange.ubc.ca, Alvin Albrecht at
aralb...@interchange.ubc.ca wrote on 18/5/00 6:37 am:

> Andrew Owen wrote:

>> OK, but I still need to know which ports are free: does anything use:

>> 00h, FFh, 4FFDh, FFFFh

> 00: the ula responds to anything even
> ff/ffff: if I remember right, Arkanoid uses this
> ghost port to read screen bytes fetched by the
> ula.
> 4ffd: did you check pera putnik's site?  He has info there
> on how the spectrum decodes xxfd.

Yeah I checked, but I'm still pretty much mystified.

> As a matter of fact, Pera has a list of likely
> candidates for port addresses.

Not on the site. Only the fact that whatever address you use the chances are
that all but three bits of the low-byte will trigger something else.

I guess it'll have to be one of the addresses 00-FF anyway so what about:

01 - Bound to be used by something
02?  
31 - Evil Kempston joystick?
FD - I think it's used by some disk interfaces

What about E0 or E1?

-Andrew


 
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