Blast from the past. Remembering: The ZX81

[Rob]

http://www.geeksaresexy.net/2009/10/16/remembering-the-zx81/

Remembering: The ZX81


"And how you could possibly resist a machine that, 28 years later, is
listed on Wikipedia with the note “There was a bug present in the
original ZX81 ROM that resulted in the square root of 0.25 being
calculated as 1.3591409 rather than 0.5.” Sure beats the red ring of death."

[Clocky]

Post by Rob
http://www.geeksaresexy.net/2009/10/16/remembering-the-zx81/
Remembering: The ZX81
"And how you could possibly resist a machine that, 28 years later, is
listed on Wikipedia with the note “There was a bug present in the
original ZX81 ROM that resulted in the square root of 0.25 being
calculated as 1.3591409 rather than 0.5.” Sure beats the red ring of
death."

I still use a 4kb Tandy TRS-80 MC-10 on IRC from time to time.

[Hunter]

Post by Clocky

Post by Rob
http://www.geeksaresexy.net/2009/10/16/remembering-the-zx81/
Remembering: The ZX81
"And how you could possibly resist a machine that, 28 years later, is
listed on Wikipedia with the note “There was a bug present in the
original ZX81 ROM that resulted in the square root of 0.25 being
calculated as 1.3591409 rather than 0.5.” Sure beats the red ring of death."

I still use a 4kb Tandy TRS-80 MC-10 on IRC from time to time.

I've still got the expansion interface from my old TRS80 Model I
floating around, it was bigger than the bloody computer. Alas the
computer is long gone so it's purely a nostalgic brick.

[Don McKenzie]

Post by Hunter
I've still got the expansion interface from my old TRS80 Model I
floating around, it was bigger than the bloody computer. Alas the
computer is long gone so it's purely a nostalgic brick.

I have my own version of a nostalgic brick:
http://www.dontronics-shop.com/is-this-australias-first-pc.html

Cheers Don...
--
Don McKenzie

Site Map: http://www.dontronics.com/sitemap
E-Mail Contact Page: http://www.dontronics.com/email
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Breakout, Prototype, Development, & Robotics Boards:
http://www.dontronics-shop.com/sparkfun-electronics.html

[Clocky]

Post by Don McKenzie

Post by Hunter
I've still got the expansion interface from my old TRS80 Model I
floating around, it was bigger than the bloody computer. Alas the
computer is long gone so it's purely a nostalgic brick.

http://www.dontronics-shop.com/is-this-australias-first-pc.html
Cheers Don...

Yeah, I was reading that... interesting story especially your custom
hardware design. The original TRS-80 models were a bit before my time, I
started on a 16k Standard BASIC CoCo2 then moved on to the same with
Extended Colour BASIC which I upgraded to 64K and also added a true
lower/upper case switch with the later 6847 VDG's were capable of
displaying. I still have that CoCo, in fact I cleaned it up just this year
and it looks like new again.

I moved onto Commodore 64/Amiga and various others later, and made some
interesting (to me at least) projects some of which are on this website;

www.users.on.net/~clockmeister

[Don McKenzie]

Post by Clocky
Yeah, I was reading that... interesting story especially your custom
hardware design. The original TRS-80 models were a bit before my time, I
started on a 16k Standard BASIC CoCo2 then moved on to the same with
Extended Colour BASIC which I upgraded to 64K and also added a true
lower/upper case switch with the later 6847 VDG's were capable of
displaying. I still have that CoCo, in fact I cleaned it up just this year
and it looks like new again.

:-)

I also did 64K upgrade kits and lower case for the tandy CoCo, but the
doco got lost over the years, as I migrated to newer systems. My CoCo
lower case was a plug in board, removed the 6847, and plugged it into my
PCB, then the PCB into the 6847 socket.

Post by Clocky
I moved onto Commodore 64/Amiga and various others later, and made some
interesting (to me at least) projects some of which are on this website;
www.users.on.net/~clockmeister

Yes, a good reason to document what was done in the early days of
Australian computing, otherwise it gets lost forever.

The DSE VZ300 rom was almost a direct copy of the TRS-80 model one,
level 2. I played around with the VZ a fair bit also.

Looks like you just missed the TRS-80 Model one by a couple of years
Clocky, as your interests start just after this period, and follow a
very similar path to where I went, as did many others, I'm sure.

I just visited:
http://members.ozemail.com.au/~bconlon/
ATL Totalisator history, which is where I spent 25 years of my life.
brought back a few memories, but seems like ancient history now.

Cheers Don...
--
Don McKenzie

Site Map: http://www.dontronics.com/sitemap
E-Mail Contact Page: http://www.dontronics.com/email
Web Camera Page: http://www.dontronics.com/webcam
No More Damn Spam: http://www.dontronics.com/spam

Breakout, Prototype, Development, & Robotics Boards:
http://www.dontronics-shop.com/sparkfun-electronics.html

[Nick Andrew]

Post by Don McKenzie
http://www.dontronics-shop.com/is-this-australias-first-pc.html

I might have to challenge you for the "most modified" label, Don. My
System-80 got a lot of homebrew modifications in its day. It gradually
became the Zeta RTRS, then Zeta BBS, which evolved into the Kralizec
Dialup Unix System, finally renamed to the somewhat more memorable
Zeta Internet.

I don't have any description online but pictures are at:

http://www.nick-andrew.net/System80/Gallery/512x384/index.html

The rough list of modifications was:

- lower case (custom character generator in EPROM)
- Paged 256K RAM (1K pages)
- system speed up
- real time clock
- D-A converter for sound
- RS-232 interface
- Custom ROM
- Circuitry to avoid streaks on the screen during updates
- Reduced wait states on memory access
- Circuitry to control a dumb modem to answer/hangup & read the Carrier Detect signal
- Detachable keyboard and joystick
- Additional keys on the keyboard
- Extended capacity power supply

Also:

- Errol Rosser Double Density floppy disk controller

Nick.

[Don McKenzie]

Post by Nick Andrew
I might have to challenge you for the "most modified" label, Don. My
System-80 got a lot of homebrew modifications in its day. It gradually
became the Zeta RTRS, then Zeta BBS, which evolved into the Kralizec
Dialup Unix System, finally renamed to the somewhat more memorable
Zeta Internet.

Thanks for sharing Nick,
Your installation techniques are very reminiscent of my efforts. :-)

my friend Mick Gulovsen had the sys-80 version of mine. Every mod I
installed, he also proved on the sys-80.

I came up with the 32 chr mode video display for the sys-80, which was
printed in Micro-80 mag.

Mick had trouble getting the top on his unit, because of the birds nest
of wiring, and it lived with the top cover just sitting up in the air,
off from the keyboard.

Post by Nick Andrew
- Errol Rosser Double Density floppy disk controller

now there is a name that rings a bell. And sydtrug with the bridge logo.
would have to be the oldest computer user group in Australia.
Michael Cooper still around?

I was more tied up with Adelaide Micro-80 group in the early days.

BTW, I'll send the picture link onto Mick.
I'm sure he will be very interested.

Cheers Don...
--
Don McKenzie

Site Map: http://www.dontronics.com/sitemap
E-Mail Contact Page: http://www.dontronics.com/email
Web Camera Page: http://www.dontronics.com/webcam
No More Damn Spam: http://www.dontronics.com/spam

Breakout, Prototype, Development, & Robotics Boards:
http://www.dontronics-shop.com/sparkfun-electronics.html

[Nick Andrew]

Post by Don McKenzie
my friend Mick Gulovsen had the sys-80 version of mine. Every mod I
installed, he also proved on the sys-80.

Interesting. From what I recall, the TRS-80 circuit design differed from
the System-80 in a few non-trivial ways. The basic incompatibilities
between the two machines were in Cassette I/O (port-mapped versus
memory-mapped), printer I/O and 32-character mode (TRS-80 was
software-controlled and displayed every 2nd character wide, whereas
the System-80 one was pushbutton controlled and displayed the first 32
characters wide). But as well as that, Dick Smith (EACA/LNW) skimped on
a 1-kbit RAM chip for the video display and so a lower-case mod required
a new RAM chip as well as a character generator. But for the TRS-80, I
think many of them had the necessary RAM already.

Post by Don McKenzie
I came up with the 32 chr mode video display for the sys-80, which was
printed in Micro-80 mag.

That's to make it work the same way as the TRS-80 one? Good idea.

Post by Don McKenzie
Mick had trouble getting the top on his unit, because of the birds nest
of wiring, and it lived with the top cover just sitting up in the air,
off from the keyboard.

Well he must have had more mods than me, because mine mostly fit under
the PC boards or were soldered on top of existing chips. My first 48k
mod was a laugh, with two rows of 16k chips soldered on top of the
existing chips except for two pins which were daisy-chained with hookup
wire. The later paged 256k mod got rid of all that by using 256k
chips.

Post by Don McKenzie

Post by Nick Andrew
- Errol Rosser Double Density floppy disk controller

now there is a name that rings a bell.

Errol is reachable at http://www.lan-mind.com.au/

Post by Don McKenzie
And sydtrug with the bridge logo.
would have to be the oldest computer user group in Australia.
Michael Cooper still around?

I'm not sure about Michael Cooper. Ira Goldklang may know
(www.trs-80.com)

Post by Don McKenzie
I was more tied up with Adelaide Micro-80 group in the early days.
BTW, I'll send the picture link onto Mick.
I'm sure he will be very interested.

Unfortunately a lot of them are out of focus, and I don't have the
System-80 any more :-(

Nick.

[Clocky]

Post by Nick Andrew

Post by Don McKenzie
http://www.dontronics-shop.com/is-this-australias-first-pc.html

I might have to challenge you for the "most modified" label, Don. My
System-80 got a lot of homebrew modifications in its day. It gradually
became the Zeta RTRS, then Zeta BBS, which evolved into the Kralizec
Dialup Unix System, finally renamed to the somewhat more memorable
Zeta Internet.
http://www.nick-andrew.net/System80/Gallery/512x384/index.html
- lower case (custom character generator in EPROM)
- Paged 256K RAM (1K pages)
- system speed up
- real time clock
- D-A converter for sound
- RS-232 interface
- Custom ROM
- Circuitry to avoid streaks on the screen during updates
- Reduced wait states on memory access
- Circuitry to control a dumb modem to answer/hangup & read the Carrier Detect signal
- Detachable keyboard and joystick
- Additional keys on the keyboard
- Extended capacity power supply
- Errol Rosser Double Density floppy disk controller
Nick.

That's really cool Nick. I'm always amused when I hear people talk about how
they "built" a PC... they really have no idea in a historic sense what it
really meant to build your own computer.

[Don McKenzie]

Post by Nick Andrew
I might have to challenge you for the "most modified" label, Don. My
System-80 got a lot of homebrew modifications in its day. It gradually
became the Zeta RTRS, then Zeta BBS, which evolved into the Kralizec
Dialup Unix System, finally renamed to the somewhat more memorable
Zeta Internet.

Hah! Looking at your pictures Nick, I just remembered those crazy hard
plastic inter-connect cables between boards on the sys-80.

Every time we spun the boards over, we had to re-solder them. Eventually
replaced them with flat ribbon cable. In fact the rainbow coloured cable
you used a lot on your wiring mods.

DSE or Rod Irving must have stocked it at the time.

I remember DSE, when they stocked electronics components. (a month ago) :-)

I went into the two DSE stores at Broadmeadows Vic today. Not a resistor
in sight. And the smaller store looks like it is hanging out for
Christmas, as it is almost bare right now.

I'll bet it shuts down in the new year, after they move a truck load of
toys.

Cheers Don...
--
Don McKenzie

Site Map: http://www.dontronics.com/sitemap
E-Mail Contact Page: http://www.dontronics.com/email
Web Camera Page: http://www.dontronics.com/webcam
No More Damn Spam: http://www.dontronics.com/spam

Breakout, Prototype, Development, & Robotics Boards:
http://www.dontronics-shop.com/sparkfun-electronics.html

[Marts]

Don McKenzie wrote...

... or Rod Irving must have stocked it at the time.

Oh god, there's a blast from the past. Even I bought some stuff from that store.
I think that it was a side street at the top end of Elizabeth St in Melbourne,
wasn't it?

I went into the two DSE stores at Broadmeadows Vic today. Not a resistor
in sight. And the smaller store looks like it is hanging out for
Christmas, as it is almost bare right now.
I'll bet it shuts down in the new year, after they move a truck load of
toys.

We have a Woolworths run DSE in town now. When I was in there I asked the woman
who was an 'area manager' what was the go as we'd seen a dozen DSE stores come
and go, same with Tandy. She said that yes this was a concern with franchise
operators. So what they were starting to do was to run them as a part of the
corporation's operations, rather than leasing franchises to independant
operators.

I wonder if the stores that you speak of are the older franchise setups.

[Nick Andrew]

Post by Marts
Don McKenzie wrote...

... or Rod Irving must have stocked it at the time.

Oh god, there's a blast from the past. Even I bought some stuff from that store.
I think that it was a side street at the top end of Elizabeth St in Melbourne,
wasn't it?

Rod Irving was also in York St, Sydney, if I recall correctly. Along with David
Reid.

Nick.

[Nick Andrew]

Post by Don McKenzie
Hah! Looking at your pictures Nick, I just remembered those crazy hard
plastic inter-connect cables between boards on the sys-80.

Yes, what a nuisance they were. The reliability was very poor.

Post by Don McKenzie
Every time we spun the boards over, we had to re-solder them. Eventually
replaced them with flat ribbon cable. In fact the rainbow coloured cable
you used a lot on your wiring mods.

I used to buy a lot of ribbon cable. My keyboard detached eventually
with a DB25 plug/socket pair but I found using it with my "extension
cable" made it unreliable. No doubt it wasn't meant to drive metres
of signal without any twisted pairs, etc.

Post by Don McKenzie
DSE or Rod Irving must have stocked it at the time.
I remember DSE, when they stocked electronics components. (a month ago) :-)

I remember DSE when they were staffed by enthusiasts, although it was
more like 29 years ago. When I started to need parts that DSE didn't
stock I would go to Sheridan Electronics in Redfern. Once I even picked
up a part in Japan (Akihabara) which I was unable to source in Australia.

Post by Don McKenzie
I went into the two DSE stores at Broadmeadows Vic today. Not a resistor
in sight. And the smaller store looks like it is hanging out for
Christmas, as it is almost bare right now.

Jaycar have picked up a bit where Dickie's left off, although they (Jaycar)
also stock a lot of toys and cheap knick-knacks. I found the Blacktown
Jaycar store was staffed with enthusiasts. One staff member told me he
started working there because his wife complained he was spending all of
his free time in there (as a customer). So he killed two birds with one
stone.

Post by Don McKenzie
I'll bet it shuts down in the new year, after they move a truck load of
toys.

Ouch, that barb hurt!

Nick.

[terryc]

Post by Nick Andrew
When I started to need parts that DSE didn't
stock I would go to Sheridan Electronics in Redfern.

Was that the "surplus" shop on Elizabeth st?

[Nick Andrew]

Post by terryc

Post by Nick Andrew
When I started to need parts that DSE didn't
stock I would go to Sheridan Electronics in Redfern.

Was that the "surplus" shop on Elizabeth st?

Could be. They had all kinds of unusual kit in store.

Nick.

[Clocky]

Post by Nick Andrew

Post by Don McKenzie
Hah! Looking at your pictures Nick, I just remembered those crazy
hard plastic inter-connect cables between boards on the sys-80.

Yes, what a nuisance they were. The reliability was very poor.

Post by Don McKenzie
Every time we spun the boards over, we had to re-solder them.
Eventually replaced them with flat ribbon cable. In fact the rainbow
coloured cable you used a lot on your wiring mods.

I used to buy a lot of ribbon cable. My keyboard detached eventually
with a DB25 plug/socket pair but I found using it with my "extension
cable" made it unreliable. No doubt it wasn't meant to drive metres
of signal without any twisted pairs, etc.

Post by Don McKenzie
DSE or Rod Irving must have stocked it at the time.
I remember DSE, when they stocked electronics components. (a month ago) :-)

I remember DSE when they were staffed by enthusiasts, although it was
more like 29 years ago. When I started to need parts that DSE didn't
stock I would go to Sheridan Electronics in Redfern. Once I even picked
up a part in Japan (Akihabara) which I was unable to source in
Australia.

Post by Don McKenzie
I went into the two DSE stores at Broadmeadows Vic today. Not a
resistor in sight. And the smaller store looks like it is hanging
out for Christmas, as it is almost bare right now.

Jaycar have picked up a bit where Dickie's left off, although they
(Jaycar) also stock a lot of toys and cheap knick-knacks. I found the
Blacktown Jaycar store was staffed with enthusiasts. One staff member
told me he started working there because his wife complained he was
spending all of his free time in there (as a customer). So he killed
two birds with one stone.

I worked at DSE only a few years ago and I knew the writing was on the wall
for DSE as an enthusiasts electronics store when I was the only person there
who helped any customer venturing anywhere near the "P" (component) section
and actually cared about their projects and offered advice where I could.
Having said that, my local Jaycar are staffed by clueless (EPROMs?... nah
nobody uses them anymore, everyone uses PIC's now - you can use those
instead) numpties also although I have noticed that at other stores the
staff are pretty knowledgeable so it varies from store to store.

[Marts]

Clocky wrote...

Post by Clocky
That's really cool Nick. I'm always amused when I hear people talk about how
they "built" a PC... they really have no idea in a historic sense what it
really meant to build your own computer.

Even historically it's not really building. It's a matter of assembling one. Buy
the motherboard, buy the RAM, get the CPU, a video card, a hard disk, a power
supply and a case to put it all in.

Guys who introduced me to computing at work all built their own from kits, as I
understood it at the time.

They even wrote their own programs or copied them from magazines or books,
assembled them, compiled them, ran the tape to execute them and so on.

Today's kids may find all this extremely tiresome but for these guys this was it
was all about.

[David]

Post by Marts
Clocky wrote...

Post by Clocky
That's really cool Nick. I'm always amused when I hear people talk about how
they "built" a PC... they really have no idea in a historic sense what it
really meant to build your own computer.

Even historically it's not really building. It's a matter of assembling one. Buy
the motherboard, buy the RAM, get the CPU, a video card, a hard disk, a power
supply and a case to put it all in.
Guys who introduced me to computing at work all built their own from kits, as I
understood it at the time.
They even wrote their own programs or copied them from magazines or books,
assembled them, compiled them, ran the tape to execute them and so on.
Today's kids may find all this extremely tiresome but for these guys this was it
was all about.

It is a bit like the good old days when youngsters could only afford to
buy an old bomb to run around in.

My first computer was an Exidy Sorcerer, which really impacted on my
budget as I was at Uni on TEAS.

I really wanted a word processor, but no way I could afford one - so
learnt assembly and wrote one, though it was very simple and rather
crude.

Since I also couldn't afford a printer, I had to write out my essays and
assignments on it, then copy off the screen (using a little B&W TV as a
monitor) to type them out on a typewriter.

Ah, those good old days

David

[Nick Andrew]

Post by David
My first computer was an Exidy Sorcerer, which really impacted on my
budget as I was at Uni on TEAS.

I would have killed for a Sorcerer :-)

Nick.

[terryc]

Post by Marts
Even historically it's not really building.

Nope, you soldered all the individual components on onto the circuit
board.

[Nick Andrew]

Post by Clocky
That's really cool Nick. I'm always amused when I hear people talk about how
they "built" a PC... they really have no idea in a historic sense what it
really meant to build your own computer.

Yeah, if it didn't require soldering and circuit debugging, it's not really
"building" :-)

Nick.