From: cs171wat@sdcc5.ucsd.edu (Jack Dietz)
Newsgroups: alt.folklore.computers
Subject: Re: Sinclair Lore Query
Date: 17 Apr 92 19:28:55 GMT

In <1992Apr16.021018.28122@descartes.waterloo.edu> dagbrown@descartes.waterloo.edu (Dave Brown) writes:

>In article <1992Apr13.094328.1@mdcbbs.com> rivero@mdcbbs.com writes:
>>
>>  Found a working Sinclair with memory expansion and some tape programs 
>>for $5 at a yard sale over the weekend. Anyone have interesting stories about
>>this little machine?
>>
>I remember using one of those!  Is it the ZX80, ZX81, or the Spectrum?

>I remember when the Spectrum first came out it was billed as featuring
>"color and sound"  .  Not "more colors" or "Better sound..."   just
>"color and sound."  The ZX80 had about 1K of RAM, and the ZX81 had a tiny
>amount more and a calculator keyboard (not just a flat
>piece of plastic...).  At any rate, I encountered a Spectrum
>that had a real keyboard added to it (not one of the Trademark Squishy
>Rubber Deals that Sinclair are famous for) and I found, to my
>dismay, that I could actually type _faster_ than the machine...and
>my typing wasn't any good then anyways (like it's any good now!)

Hey.  You could get sound out of the machine, since the processor
was directly twiddling the RF modulator.  It took a LOT of work and
the code wasn't very friendly (you tended to get noise on the
screen) but sound DID exist.  Color?  No 3.58 MHz crystal, but you
could probably add it with a couple of chips and some mind sweat.

>Also, every code in its ASCII table was something...like a BASIC
>command, so you could put machine code programs in REM statements
>at the beginning of a BASIC program and actually have it printable
>so you could, say, put a program listing in a magazine with
>machine code in it.  Didn't they run off Z80s?  Terrible
>machines, though....

Most micro BASICs used some internal code for each keyword.  What
made the ZX81's BASIC unique was that they were displayable
characters.  Characters 0-63 were the upper-case alphabet etc,
128-191 were the inverses of those.  Then 192-255 were things like
PRINT, LIST, TO (as in FOR-TO), AND, EDIT, and so on.  If you just
dumped machine code to the screen you'd end up with very verbose
garbage because of this.  One of the ramifications of that is that
they wanted to save on operators.  An example is the lack of LEFT$,
RIGHT$ and MID$.  Instead, by typing 'A$(5 TO 7)' you got the effect
of MID$(A$, 5, 3) on, say, MS-BASIC for the PET.  Odd.

The ZX81 was Z80 based.  It had four chips.  1) A raw Z80 (no ports
or anything).  2) An 8K BASIC ROM.  3) A 1K static ram chip
(upgraded to a whole 2K in the Timex/Sinclair 1000).  4) A glue chip
with everything else they needed.  The glue chip was supposed to
replace about 15 TTL chips, so it wasn't high science or anything.
And, no, the ZX81 did not come with a calculator style keyboard.
People _sold_ calculator-style keyboard overlays for ten bucks or so
that you'd stick onto the membrane keyboard and type on.  Then there
were the kits where you took it out of the case and put it inside a
bigger box with a keyboard.  THEN there was the keyboard that
plugged into the backplane, except that they couldn't get all of
the keyboard lines that way so it had to be placed where it could
pick up RF emissions from the computer!

It worked.  Barely.  And I'm amazed it did.  :)

>				Dave Brown
>				dagbrown@descartes.waterloo.edu
>				I'd rather be using TECO.
--
Jack Dietz                             "I have a cunning plan..." -- Baldric
// jdietz@ucsd.edu