Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!bloom-beacon!eru!luth!sunic!mcsun!ukc!icdoc!inmos!inmos-is!gary
From: gary@brb.isnet.inmos.co.uk
Newsgroups: comp.sys.atari.st
Subject: ZX81 Emulator was Re: Z80 cross assembler/Emulator
Message-ID: <140.26d302a9@brb.isnet.inmos.co.uk>
Date: 22 Aug 90 22:09:44 GMT
References: <1990Aug3.185119.848@newcastle.ac.uk> <21393@duke.cs.duke.edu> <2172@cernvax.UUCP>
Organization: Inmos Limited
Lines: 64

In article <2172@cernvax.UUCP>, dougie@cernvax.UUCP (douglas mclaggan) writes:
> On a similar note to the above, does anybody know whether an emulator for
> a Z80 machine exists for the ST?  I thought I heard of a ZX Spectrum emulator
> for the Amiga, but I'm not sure if this is true.  Also, what about that Z80
> cross-compiler - does anyone have a copy of it?
> -- 
> +---------------------------------------------------------------------------+
> | Dougie McLaggan. ->->-> 'dougie@cernvax.cern.ch', or 'dougie@cs.hw.ac.uk' |
> +---------------------------------------------------------------------------+

There is a very intersting piece of software which has become available at
most (UK) public domain software distributors - a Sinclair ZX81 emulator for
the Atari ST!

For those of you who are not familiar with the ZX81... 

The ZX81 was (Uncle) Clive
Sinclairs followup to his ZX80 home computer. The ZX81 (like the ZX80)
was available in kit or pre-built form, and boasted a Z80 CPU, 1k of RAM
(16k if you bought the slot on RAM pack - which suffered from the infamous
"wobble"), a membrane keyboard with each key boasting no less than 5 or 6
functions (!), 16K (?) ROM with built in BASIC. The ZX80 was released in
1980, and was arguably the computer which set alight the UK home computer
scene. Although the ZX80 could display a steady picture on the TV screen
there was a loss of sync every time a key was pressed and also every time
a program was run, because Uncle used the Z80 CPU to refresh the screen when
it wasn't otherwise busy. The ZX81 released in 1981 fixed this, although still
maintained a FAST mode for running programs, where the screen would disappear
ala ZX80.

The ZX81 emulator is supplied with a number of ZX81 games (originally they
came on cassette) thankfully loaded from disk. The copyright situation of
the games and ZX81 ROM code may be dubious, but I doubt if more than a
handful of people still use this beast (I recently saw one sold at an 
auction for a single pound!). Pressing the ST HELP key displays a very
clear graphic of the ZX81 keyboard - this is essential as single keypresses
enter multiple characters e.g. pressing "K" prints LOAD " on the screen
(you then type the filename normally). The emulator emulates the 1k, 16k
or 48k (wow) machines. Some of the games which fitted into the 1k, put
some of the ST gargantuans to shame. The emulator also correctly emulates
the FAST mode mentioned above.

It has to be seen to be believed.

You could if you wished program the Z80 in assembler (in fact there may have
been one on the disk). The normal way to load a machine code program was to
have a REM statement as line 1 with lots of characters (more than the length
of your machine code), then poke the machine code into RAM byte by byte (in
decimal!) which would overwrite the characters following the REM statement.
When listed it looked like total gobbledegook, as the machine expanded out
each byte into its token textual value. Believe me it wasn't easy (it was
easy to crash the machine though! and the only way to reset the computer
was by pulling out the power supply plug!!!!!!) 

Sigh! Those were the days. I wanted a ZX81, but couldn't afford one, so I had
to stick to my ZX80.

--Gary 
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Gary Morton   Inmos Ltd, Aztec West, Bristol | EMail(UK) 
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The opinions above are my personal views     | EMail(ROW)
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