ZX81/TS1000 and/or Spectrum?

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
tdg8934
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ZX81/TS1000 and/or Spectrum?

Post by tdg8934 »

My first computer at 17 was the TS1000 2K in the USA. I built it as a kit and later went on to other computers such as the Atari 400, 800XL, 800CE; Apple 2; Tandy and color computer, Commodore C64, SX-64; Amiga 500, 3000, etc. The TS1000 was my first and most memorable. Over the years I have purchased 1-2 of them on ebay and moved and lost track. In the last couple of years I have been privileged to spend time with them again learning assembly language when time permitted but only due the ZXPand wonderful product! I messed with the firmware a bit with Charlie's help and was even able to connect it to an LCD screen and send data. It seems I'm always looking to try different things in technology and see what can and can not be done with them as this interests me a lot. I have worked with a few micro-controllers over the years too such as the Arduino and variants like Teensy 2/3 as well as many Parallax ones like the Basic Stamp 2, SX-28, 48/52, and a few variants of their Propeller multi-core processor. I have been very interested in projects dealing with LED displays and have built some wonderful displays in RGB with other peoples code that I modified. As a trained Electrical Engineer, I have a moderate but not strong software background in development for fun projects but can figure out most software to modify them for my means. So this is my background and history.

I still have a couple of TS1000s with new video circuits and a ZXPand and now my new ZeddyNet card to go out to the internet. I never really had the opportunity to buy a Spectrum when I was younger as it just wasn't sold in the USA that I knew of. I am curious about them and how they differ from the ZX81 besides just the color aspect and perhaps more memory. I would be interested in learning more about them and what is available technology wise (i.e. ZXPand) for them. Where do I start on this to purchasing one (I.e. Ebay?) and making sure it will work with a video monitor (or what I use is a video capture device to an open window on my laptop).

Thanks for reading...

Tim
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RetroTechie
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Re: ZX81/TS1000 and/or Spectrum?

Post by RetroTechie »

Hello Tim,

I'd like to think of the ZX Spectrum as a ZX81 with all the bits added to make it a 'proper' :lol: home computer:
  • Color.
  • Sound.
  • An ULA that produces screen output without help from the Z80. Read: 100% CPU time useable vs. ~25%, making the Spectrum 4x (or so) faster.
  • Fixed layout of the video RAM, no hardware mods or difficult tricks needed to use hi-res.
  • More RAM (16K min, 48K standard, 128K models also exist).
  • 128K models also have a proper soundchip (vs. a simple beeper on the 16/48K models).
  • Better keyboard. Still poor, but better than the ZX81's. :mrgreen:
  • For Z80 programmers, pretty easy to understand how the hardware works.
But for using real hardware, I really wouldn't bother with original 16/48K models. They're fragile, if they aren't broken already chances are they will in short order. Much can be fixed (eg. replacement keyboard foils), but you'd need to do a lot of modding to get a reliable machine. That is: until the ULA dies, replacement stocks for that IC have run out a while ago. The 128K ("toastrack") is a little better in that respect, but a complex circuit. The Amstrad-made +2(A), +3(A) models are built much better. But all the 128K models are relative hard to find & expensive (and some incompatibilities between them).

In terms of storage, there's many options. Including ones that use modern flash cards. That's generally the case for Spectrum peripherals: if you can imagine it, there's probably someone who built it and hooked it up to Spectrum. :D

I'd have a go at some programming on emulators first. Not the least for the debugging facilities that some emulators include. For some 'geek cred' ;) you could do that on a Raspberry Pi for example. Then if at some point you feel an itch to use real hardware, look for a modern clone. Just some examples: Besides a variety of FPGA boards like the Myst board, V6Z80P (Retroleum), Arcade Replay board, Altera DE1, etc etc (many more to come). And there's the ZX Spectrum Vega, but at this point it remains to be seen how hackable/programmable that is.

Any of those is likely nicer hardware to work on. Not as likely to break down, and comes with many goodies like SD card readers, joystick ports (or trivial to wire up), and so on. The "rubber key" 16/48K models are more for the 'hardcore' folks used to all the problems with these machines, or for collectors who stuff 'em in a box and just look at it from time to time. ;)
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1024MAK
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Re: ZX81/TS1000 and/or Spectrum?

Post by 1024MAK »

First, best get this off by chest first :lol: for all things ZX Spectrum, at least browse World of Spectrum. Even though parts of the site are operating in a degraded mode (a new site is under construction), it is still a great resource. There are lots of useful posts in the WoS forums in amongst the general chit-chat. For example, the hardware forum.

As referred to above, the ZX Spectrum is a machine that has a lot of improvements compared to the Zeddy. The bit about the CPU always running at 100% is not true however. When accessing the 16k bytes of RAM where the screen is located is sometimes slower than accessing the higher 32k bytes of RAM, or the ROM. The slowdown occurs only when the ULA requires priority access to read screen data in order to form the video picture. It is known as contention.

The cheapest ZX Spectrums are the ZX Spectrum+ models (may be 16k byte or 48k byte boards, as Sinclair offered the keyboards as upgrades). Both the rubber key and the ZX Spectrum+ models suffer from life expired keyboard membranes. By RWAP has both in stock. They are not hard to replace.

I have only repaired a small number. But I do often try to help others in the WoS hardware forum. It appears the most common faults are DRAM faults and faults caused by either the DRAM chip killing the internal power inverter circuit, or by (past) abuse of the machine (removing/fitting an expansion, or interface while powered up, or using the wrong "AC adaptor" / power supply unit). If abused, the ULA and/or the CPU may be damaged.

Yes, the ULA used in the 16k/48k models (including the Spectrum+) is no longer available. But as long as it has not been abused, they appear to be relatively reliable. Of the used computers that I have bought, so far, I have not had a defective ULA in a Soectrum. But I do have two ZX81s with defective ULAs. .

The normal output of the rubber key and Spectrum+ models is RF in the UHF band. So you would need to modify one to output composite video instead. This should be easy for you. If your video capture device can lock on and convert a 625 line, 15625Hz / 50Hz PAL colour encoded signal, it most likely will be fine with the output from a Spectrum.

The 128k models all already have a composite video output on the RGB/monitor DIN socket (but the pin out differs between different 128k models).

In any event, of course ensure the machine is working before buying. As although there are at least two repairers or operating in the UK, that is of limited value to you.

One other thing, is is strongly recommended that all the electrolytic capacitors on the main board are renewed. As the originals are beyond their service life. Failure of one of these in the internal power inverter circuit can cause damage to other components like DRAM chips.

There are various mass storage devices available. In recent years we have SD and micro SD being used. Before that CF cards. And there are also a number of disk interfaces.

Some of these expansions include joystick interfaces.

Right, that's enough for now :mrgreen:

Mark
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tdg8934
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Re: ZX81/TS1000 and/or Spectrum?

Post by tdg8934 »

Thanks for the excellent background on the Spectrum guys!

I have started to look closely today at the FPGA MIST because it support so many of the original computers I used as listed in my original post. It's pricey and shipping isn't great to the USA but worth investigating. Does anyone have one that can share their experiences?

Thanks,

Tim
tdg8934
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Re: ZX81/TS1000 and/or Spectrum?

Post by tdg8934 »

I just ordered a MIST FPGA Computer for Spectrum hardware emulation (as well as a lot more other computers) and an SD card for $252 USD.

http://www.lotharek.pl/product.php?pid=96

I hope I won't be disappointed but the video's on his site look really good!

Tim
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Re: ZX81/TS1000 and/or Spectrum?

Post by questarian »

I'm in the US as well, and I had been curious about the ZX Spectrum since I'd heard of them in the 80's. Finally got around to buying a few off of ebay, and several of the modern SD interface card... and all totaled, with the international shipping and PAL/RGB converters, it would have been about the same cost to do it FPGA emulated.

I have to admit to being an original hardware chauvinist/masochist... there nothing like working with original hardware, except for have to repair them. New keyboard membranes, driving myself crazy adjusting a series 2 48k Speccy to get the video working (sort of), new keyboard faces, and the ever looming promise of hardware failure... but then, that's all a part of the retro computing experience isn't it.

Still, they're wonderful little machines which I don't regret buying.

-John-
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Re: ZX81/TS1000 and/or Spectrum?

Post by 1024MAK »

You're not a salesman are you :lol:

Mark
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questarian
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Re: ZX81/TS1000 and/or Spectrum?

Post by questarian »

1024MAK wrote:You're not a salesman are you :lol:

Mark
Is that a statement or a question? :lol: ... either way I'll stick with (8 bit) masochist.

Honestly, I'm never sure what's the biggest risk, 30+ year old hardware or the new stuff... FPGA emulators are expensive, FAR less easy, if not impossible, for the average hobbyist to repair, the cores are rarely 100% compatible or cycle perfect reproductions of the original machines, and there's no guarantee that development of the boards, or the emulation cores, won't end abruptly... and I won't even get into the community drama that can occur over these sort of hobbyist endeavors.

At least the old tech still looks cool sitting on a shelf.

-John-
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Re: ZX81/TS1000 and/or Spectrum?

Post by 1024MAK »

And it's more fun tinkering with the original hardware :lol:

Know what you mean :D

Mark
ZX81 Variations
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ZX81 Video Transistor Buffer Amp

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Re: ZX81/TS1000 and/or Spectrum?

Post by RetroTechie »

questarian wrote:Honestly, I'm never sure what's the biggest risk, 30+ year old hardware or the new stuff... FPGA emulators are expensive, FAR less easy, if not impossible, for the average hobbyist to repair,
No argument there. Point is more that a (new, or good-as-new) FPGA board is less likely to break in the first place, within, say 5 or 10 years from purchase. And while the old hardware may seem easier to repair, that entirely depends on what breaks. And there's a lot that can break in a 30+ year old machine... :( Not to mention that repairs can take a lot of time (+tools, and parts), and include fault-finding which can take even more time. That's not talking about finding (working!) vintage parts vs. finding another FPGA board to do the job.
the cores are rarely 100% compatible or cycle perfect reproductions of the original machines,
True. But for most popular systems, there are very accurate cores around now. And even if not 100% accurate, they'll still run most software (read: at least those titles that people care about). It depends more on what soft cores are available for a particular FPGA board. When not, a core may be easily ported by some people. But for most users, that's very much non-trivial even if the Verilog / VHDL code is out there.
and there's no guarantee that development of the boards, or the emulation cores, won't end abruptly...
Also true. But in that case, you can still continue to use what works @ that point. For at least as long as that particular FPGA board lasts.

For example, I own a 1chipMSX. Granted, there's nothing like sitting in front of a genuine Japanese MSX2+ machine or MSX Turbo-R. :D But that 1chipMSX runs practically all MSX software I throw at it. It's compact / lightweight / easy to carry. It doesn't run hot. There isn't much on the board besides FPGA, RAM, a few small IC's and some voltage regulators. It includes an SD card reader, VGA output, various ROM mappers, more RAM than you'll ever need, audio extensions and other goodies. Keyboard is PS/2 so easy to replace. And the soft core is up to MSX2+ now & still being developed / bugfixed / improved. Regardless of taste, easily the best MSX computer I own.

I think both original hardware and modern implementations have their place. And for some uses, there's considerable overlap. But going forward, reality is those old machines will die some time. When (not if!) that happens, things like FPGA implementations are all that's left.
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