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mahjongg
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Re: My ZX81 clone now called "ZX81+34"

Sun Feb 28, 2016 3:57 pm

Finally, I got it working:

After I "blew up" my first effort by applying the power supply voltage the wrong way around, I designed version 2.0 adding many improvements, (and renamed it ZX81+35 because we are a year later now :? ) and yesterday I was rewarded with the first sign of life from it.

Image

Its still far from perfect, in fact the keyboard was all wired up wrong (manual wiring) so I had a hard time to even enter

Code: Select all

10 PRINT "HALLO WORLD"
and run it, but I did (note the Dutch way to write "hello" is "hallo" :) ).

if you want to know more about my effort you can read it on my webpage, here: https://revspace.nl/ZX81%2B34

blc
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Re: My ZX81 clone now called "ZX81+34"

Tue Mar 01, 2016 2:22 pm

Congratulations, this is some impressive work.

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Re: My ZX81 clone now called "ZX81+34"

Thu Mar 03, 2016 11:59 pm

I now have the keyboard fully working, this enabled me to write a few test programs, which revealed further issues, its seems black and white pixels are not equally wide, and the ZX81+35 seems to have problems displaying the full character set. I'm still investigating the issues. Like I said, progress is documented at my RevSpace pages.

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Re: My ZX81 clone now called "ZX81+34"

Fri Mar 04, 2016 1:45 pm

well done. I've been following your project for a while now as I love seeing the classic 8-bitters.
Tony

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Re: My ZX81 clone now called "ZX81+34"

Mon Mar 07, 2016 3:36 pm

Display is now working well, saturated blacks and whites, and stable sync, although looking with a scope at the signal I see there is still scope :D for improving the signal.

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Re: My ZX81 clone now called "ZX81+34"

Mon Mar 07, 2016 3:51 pm

I'm very impressed with your ZX81 clone! 8-)

My real interest in home computers started with a ZX81 in kit-form in 1981, or was it 1982? It was great fun to build and little else since has compared to the joy of watching it boot up perfectly on the first attempt. Well, it made this geek incredibly happy anyway. :D

I returned to the ZX81 world a couple of years ago by buying one with a mint condition exterior but dodgy RAM off eBay for £15 with a box of assorted extras. The 1KB of RAM was ripped out and replaced with a 32KB static RAM chip (2x 16KB pages) and the old power-hungry Z80 was replaced with a 'modern' CMOS version. Current consumption almost exactly halved, so the heatsink is far less likely to cook the keyboard now. The old PAL modulator is gone too with composite video on the output socket instead making the output look much cleaner. It still looks totally standard from the outside which was my primary goal. Internal rechargeable battery power is the next mini-project, but I'll save that for a rainy weekend.

I love what you're doing. Keep up the good work! :)
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Re: My ZX81 clone now called "ZX81+34"

Sun Mar 13, 2016 3:17 pm

rendering of the latest prototype:

Image

currently investigating some video anomalies.

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Re: My ZX81 clone now called "ZX81+34"

Thu Mar 17, 2016 12:39 am

anomalies solved, video is now correct!
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characters after fixing video problems
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Re: My ZX81 clone now called "ZX81+34"

Thu Mar 17, 2016 1:10 pm

looking good :-)
Tony

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Re: My ZX81 clone now called "ZX81+34"

Wed Mar 30, 2016 11:03 pm

Now got the cassette port working reliably, after I did ( a multi phase ) redesign.
I can now load some damn fine software, which runs fine so-far, and I can use it with my built in joystick interface, that now also runs fine. testing and improving the design is going well. :D

a detailed progress report can be found here: https://revspace.nl/ZX81+34_ZX81_clone

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Re: My ZX81 clone now called "ZX81+34"

Mon Aug 01, 2016 11:42 pm

Hi,
I've been looking at this project with great interest.
I also have started with a ZX81 when it just came out, and since that I have picked up a few more, which I still have. I am looking at one of them right now 8-)
My original ZX81 was highly modified and is unrecognizable, because it definitely doesn't look like one. The pcb was taken out of the case and I put that with a real keyboard and a more power psu in a home made wood enclosure :o
Anyway, I was seriously wondering if there is any possibility to make some modified cp/m to run on this :?: , perhaps stored in the sd card, or maybe some extension card could drive a floppy...
That would of course negate the need for the tape based storage, but if this can be made to work, good riddance :D
I ran my old zx with a 64k ram card, and rarely used basic. It was great fun to code z80 and I'd love to do some more...

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Re: My ZX81 clone now called "ZX81+34"

Fri Sep 23, 2016 7:55 pm

spkdd wrote:Hi,
I've been looking at this project with great interest.
I also have started with a ZX81 when it just came out, and since that I have picked up a few more, which I still have. I am looking at one of them right now 8-)
My original ZX81 was highly modified and is unrecognizable, because it definitely doesn't look like one. The pcb was taken out of the case and I put that with a real keyboard and a more power psu in a home made wood enclosure :o
Anyway, I was seriously wondering if there is any possibility to make some modified cp/m to run on this :?: , perhaps stored in the sd card, or maybe some extension card could drive a floppy...
That would of course negate the need for the tape based storage, but if this can be made to work, good riddance :D
I ran my old zx with a 64k ram card, and rarely used basic. It was great fun to code z80 and I'd love to do some more...
sorry for the late reply, forgot to check this thread, been busy with re-designing the ZX81+35 after I found out I rotated the edge connector 80 degrees, bummer, but I have now done the layout work for this in revision 4.0 of the layout.

to answer your question, I don't think a ZX81 can run CP/M, this is from the top of my head, but if I remember correctly CP/M requires RAM (as much RAM as possible) to reside in the lower memory map, and just a very small (as small as possible) are for ROM Video and other IO. the more memory in the low region the bigger the "TPA". however the ZX-81 has a very special memory map that simply prevents this. there are computers that are ZX81 design based, and can run CP/M by modifying their memory mapping, but my ZX81+35 can not.

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Re: My ZX81 clone now called "ZX81+34"

Fri Sep 23, 2016 8:02 pm

I'm designing a PSG (ZON-X compatible sound board) expansion board for my ZX81+35, but in the course of its design I discovered I made an error in the rotation of the expansion port, and had to re-do a large part of the layout to rotate the expansion port 180 degrees.
The result of that large job is layout Revision 4.0, see below (open in new window for the full resolution).

I still have to try the expansion board, and there is still a problem with video generation in turbo mode (220% speed increase when switched to "turbo"), I plan to fix those issues, before I will release the final production files (gerber files & bill of materials, construction plans etcetera). I'm also planning a case for it.
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Re: My ZX81 clone now called "ZX81+34"

Fri Sep 23, 2016 9:35 pm

spkdd wrote:Anyway, I was seriously wondering if there is any possibility to make some modified cp/m to run on this ?
There are many homebrew Z80 machines that can do this. One I very much enjoyed building was Sergey's Zeta SBC V2. An easy build, and runs CP/M very well, along with some other more experimental Z80 multitasking OSs. Best kept in a shielded enclosure if you like listening to radio nearby, tho.
‘Remember the Golden Rule of Selling: “Do not resort to violence.”’ — McGlashan.

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Re: My ZX81 clone now called "ZX81+34"

Sat Sep 24, 2016 2:05 pm

the ZX81 class computer (one that actually runs ZX81 software, so not just a random Z80 based system) that can also run CP/M (by reconfiguring its hardware) is called the "ZXMORE", more info here:
http://www.sellmyretro.com/offer/detail ... P~~M-10247

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Re: My ZX81 clone now called "ZX81+34"

Sun Oct 02, 2016 5:12 pm

another possibility is to use one of the many retro systems based on an FPGA, that can simply re-create the old system in silicon using an FPGA.
One of the better examples is the MIST system : http://lotharek.pl/product.php?pid=96
at the moment is does not directly support any CP/M system, but it does "emulate" (not the right word) a ZX81.
As for CP/M compatibility, do remember that MSX systems can run MSX-DOS which is actually a CP/M clone with the command interface of MS-DOS, and it runs many CP/M programs fine. MIST supports MSX machines and MSX-DOS.
Also there is the commodore 128, which also runs CP/M.

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Re: My ZX81 clone now called "ZX81+35"

Tue Jul 30, 2019 11:54 pm

I recently became aware there was some interest in my ZX81 clone. I always planned to release it as "open hardware" but could not get video stable when running in "ẗurbo mode", that is at about twice the original speed, using two acceleration methods simultaneously, one method gives a 10% speed boost, another doubles the speed of the clock when not generating a picture. the first acceleration method worked fine, but with the second method enabled the video screen became unstable. Probably because I double the clock speed at the wrong moment. I intended to solve this problem, then release the design, but I got distracted.

I can now tell that I (as "mahjongg2" on github) have created a GitHub page called "ZX81plus35" (GitHub does not allow the "+" character in project names) into which I will slowly release the valid files for the latest version ZX81+35 revision 4.0
for now I have released the schematic of rev 4.0 and the Bill of materials updated to 4.0

the gerber and drill files are actually on an old windows laptop, so that will take a bit longer to upload, i will probably do that tomorrow.

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Re: My ZX81 clone now called "ZX81+35"

Wed Jul 31, 2019 11:47 am

Great stuff, thanks for sharing !
Tony

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Re: My ZX81 clone now called "ZX81+35"

Wed Jul 31, 2019 12:40 pm

You are welcome!

Keep an eye on my GitHub page, (https://github.com/mahjongg2/ZX81plus35) in the coming days/weeks I will keep adding stuff to it.

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Re: My ZX81 clone now called "ZX81+34"

Wed Jul 31, 2019 2:51 pm

mahjongg wrote:
Sun Oct 02, 2016 5:12 pm
…As for CP/M compatibility, do remember that MSX systems can run MSX-DOS which is actually a CP/M clone with the command interface of MS-DOS, and it runs many CP/M programs fine. MIST supports MSX machines and MSX-DOS.
Wait, what? I totally missed this when you said it. So MSX-DOS on an MSX2 is basically an 8-bit MS-DOS that runs CP/M programs in a (reasonably nice) BASIC interpreter shell? Whoa!
Also there is the commodore 128, which also runs CP/M.
… eventually. CP/M on the 128 is only for the patient.
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Re: My ZX81 clone now called "ZX81+35"

Wed Jul 31, 2019 11:22 pm

Now uploaded the latest know good layout (ultiboard) file, and production files (gerber and drill) so you can produce your own revision 4 ZX81+35 (PCB).

P.S. I checked the PCB files, and noticed that wat I uploaded was NOT the latest version, but I have now corrected that.

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Re: My ZX81 clone now called "ZX81+34"

Wed Jul 31, 2019 11:23 pm

scruss wrote:
Wed Jul 31, 2019 2:51 pm
mahjongg wrote:
Sun Oct 02, 2016 5:12 pm
…As for CP/M compatibility, do remember that MSX systems can run MSX-DOS which is actually a CP/M clone with the command interface of MS-DOS, and it runs many CP/M programs fine. MIST supports MSX machines and MSX-DOS.
Wait, what? I totally missed this when you said it. So MSX-DOS on an MSX2 is basically an 8-bit MS-DOS that runs CP/M programs in a (reasonably nice) BASIC interpreter shell? Whoa!
Yes, when microsoft wrote MSX-DOS (for MSX1 and MSX2) they once again copied CP/M (just like "quick and dirty DOS", they bought as the base for MS-DOS was more or less copied from CP/M86)

They only changed the basic command.com functions so you could use the COPY syntax instead of the archaic way PIP works, and other small syntax improvements.
but yes MSX-DOS is basically CP/M with MS-DOS commands, and can run CP/M software (like L80 M80, Wordstar etc) .

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Re: My ZX81 clone now called "ZX81+35" (now released on GitHub)

Sun Aug 04, 2019 4:57 pm

I now also uploaded some picture previews of the rev 4.0 PCB's; this is the top side preview as a .jpg
ZX8+35 rev 4.0 release preview top.jpg
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Re: My ZX81 clone now called "ZX81+35" (now released on GitHub)

Sun Aug 04, 2019 5:30 pm

That looks a lot harder to solder than the ZX80 I bought so many (many many) years ago :lol: At least I could cope with through hole - cannot manage this new fangled SMD type stuff at all :cry:

Must say though - the board does look neat and tidy. Signs of true love.

I was surprised that you can still buy cassette recorders (even Amazon stocks some) - I know I marked mine with snopake and covered it in tape once I had the volume just right. Oddly enough, I miss the screech of these and acoustic modems :o
Need Pi spray - these things are breeding in my house...

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Re: My ZX81 clone now called "ZX81+35" (now released on GitHub)

Sun Aug 04, 2019 5:41 pm

Andyroo wrote:
Sun Aug 04, 2019 5:30 pm
That looks a lot harder to solder than the ZX80 I bought so many (many many) years ago :lol: At least I could cope with through hole - cannot manage this new fangled SMD type stuff at all :cry:
I find SMD quite easy, apart from the really tiny components. It takes up less board space and you don't have to keep cutting leads. Just a decent magnifier and fines solder is good enough even with my old unsteady hands.

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