A proposal. Just an idea.

[sanello]

With all these cool new versions of old systems popping up like the Commander x16, C64 mini and other stuff, why not something for the Z81/TS1000? I am not talking about a spectrum here.

I would like to see something that is not an emulator, but something new with new parts. Something that only improves things they could have done when they made it and is 100% compatible.

Some ideas on what it would be like.

For practical purposes, A composite display output and an HDMI output. HDMI they couldn't do, but practical. They could have done composite though, and that's already kind of built in mostly. I don't think HDMI would be cheating too much if composite is also an option.

A clock. As I understand it, the Z80 processor can run 40mhz? Let's crank it up, but have the ability to slow it back down if we want. ZILOG still makes these things. So, awesome!

With the clock speed cranked up, a separate video card circuit to speed up things would be nice. Maybe black and white with switches for blue and white, red and white, green and white, maybe blue on light blue, maybe invert all those choices would be cool. Giving it an actual color display would be a bridge too far I think. Remember 100% backwards compatibility.

There are already new ULA's out there so, that.

An updated ROM with editing additions? A new ROM would be needed. I would not like any of the coding for programming to be changed, but a renumber command and some way to scroll through code better would be so nice. I wouldn't want to change anything about running code itself, though. Copy and paste? Also, an easy way to see how much memory you have left. Could use some secondary RAM to cache code for editing maybe?

16k native. More maybe, but keep in mind writing code to work on what most people have.

SD card saving and loading.

better voltage regulation.

A real keyboard.

What do you think?

[mrtinb]

We are very near to your suggestion with the hardware made by the German ZX-Team.

Take the ZXNU, which is a ZX80/ZX81 with No ULA, where the ULA is built from TTL ICs. It has built-in support for change between 3 ROMs. Full 56k RAM. Hires graphics support. Built-in 128k EEPROM disk. Interface for USB storage upgrade.

Pair that with the ZX-Wespi-V, that has built-in file server on a ESP32, and video output to VGA.

The German ZX-Team, has made quite some great hardware hacks during it's lifetime.

[1024MAK]

Real Zilog CMOS Z80 chips are only officially rated at 20MHz. Higher speeds are only officially available with code compatible processors (not pin or hardware compatible).

A number of modern remakes / clones / compatible computers have been made over the last five years. Some are detailed in these very forums. But not all, for example the Minstrel 3 is available here.
Most have composite video outputs. I don’t think any have HDMI video outputs.

There are various rewritten ROMs. Although they do not have all the features you list.

The ZXpand and the ZXpand+ were the best SD card interfaces for ZX81s, unfortunately the developer has not produced any for a while, and currently has no plans to make anymore.

Not sure what you mean by better voltage regulation, the 7805 can easily be replaced with a modern DC/DC converter / switching regulator.

Mark

[sanello]

Real Zilog CMOS Z80 chips are only officially rated at 20MHz. Higher speeds are only officially available with code compatible processors (not pin or hardware compatible).

Not sure what you mean by better voltage regulation, the 7805 can easily be replaced with a modern DC/DC converter / switching regulator.

Mark

That's what i meant by the regulator. I've replaced them myself. CPU speed? Crank it up to 20 then. Or use one of those derivatives as long as it can be made completely backward compatible. I know about all these other pieces and parts so it would be nice to get licenses or whatever is needed to put a new box with them integrated. I'll be taking a look at these clones that have been mentioned.

[mrtinb]

As there is no video circuit in the ZX81, the video is made in software. This requires tight timing to generate the right composite signal.

With faster CPU, the ROM routine to create the video signal has to be updated. Even though this will work for some software, many programs have their own routine that handles video. These programs will need to be rewritten to run on faster hardware.

So I cannot see how you can have faster speed, and keep compatibility.

There exists a ROM called X2, that runs on standard hardware, but the ROM routines have been updated to run faster. So software that uses the ROM routines run faster, but the programs with their own video routines still work.

[1024MAK]

Details of the Big Bang X2 ROM are in this topic.

Details of the Shoulders of Giants ROM are here.

You may also want to read about the ZX97 lite.

There are many more modern clones, do browse through the hardware section of this forum

So answer Martin‘s point, I agree, it’s not practical to have a system running a faster processor and keep full compatibly. At least, not for any machine code programs that use their own display driver code.

You can however, have a system that can run BASIC and maybe some machine code programs which use the normal ROM display system, which switches processor speed depending on which area of memory is being accessed. So the ROM code that generates the display runs at standard speed, but at other times the processor runs faster. But then you may find some of these programs unusable, because they rely on the ZX81 running at normal speed…

The above reason also makes it rather more difficult to produce a HDMI output. Such a system would have to either capture the output of the ULA or equivalent circuitry, then store in in a frame buffer (RAM) and then produce the output from this. Or do something similar to how the Chroma 81 interface does it (details here). This interface monitors the data on the ZX81 expansion port / edge-connector, and uses these signals to recreate the video signal. That is, it does not actually use the ULA video output pin.

Mark

[Moggy]

A 20Mhz ZX81 was made by Andy Rea as a one off experiment, sadly having spoken to Andy he, like Sir Morris, is not likely to be back any time soon but just for reference there is a thread about the device.

It included things such as....

QUOTE

"20Mhz Z80
128K static ram ( split into 8K pages )
the full 64K can be RAM
0-16K is fully pageable
16-48K is always pages 2,3,4,5
48-64K is fully pageable ( but during video pages 2,3 )


turbo (20Mhz)
8-16K ram wrx/udg switchable
m1not switchable

ZxPand-a-like (very very alike Thanks SirMorris) possible to page zxpand rom (once loaded to ram by special boot program) in and out

erm think thats about it... oh runs Sponzy slightly faster than original 48K spectrum !..."



Details can be found here.

viewtopic.php?f=6&t=961


Youtube video.

https://www.youtube.com/watch?v=ba8_jqBDSkU

[1024MAK]

By the way, the links to Wilf Righter’s site will fail, so use the archive site.

Mark

[stefano]

there's been plenty of development around the zx81, I'm discovering something everyday, also in the historical papers and old online articles.
To add something which wasn't mentioned yet, think at the zx1541 interface or the MEFISDOS.
viewtopic.php?t=2198
https://doczz.com.br/doc/852076/5-neues ... ommt--2--8

[sanello]

As there is no video circuit in the ZX81, the video is made in software. This requires tight timing to generate the right composite signal.

With faster CPU, the ROM routine to create the video signal has to be updated. Even though this will work for some software, many programs have their own routine that handles video. These programs will need to be rewritten to run on faster hardware.

So I cannot see how you can have faster speed, and keep compatibility.

There exists a ROM called X2, that runs on standard hardware, but the ROM routines have been updated to run faster. So software that uses the ROM routines run faster, but the programs with their own video routines still work.

That's why I suggested a video circuit (card). The speed switch I suggested would probably disable it for compatibility. Besides, I really want it to improve editing on a non emulator. This is all a pipe dream anyway. There are some really interesting options out there, though. Really want a renumber that really works on gosubs and goto and such, though I have found a couple software ways, but none seem to do it right.