Hello!

Introduce yourself to your fellow forum members - what was your journey into the Sinclair world?
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grimmware
Posts: 15
Joined: Thu Feb 04, 2021 1:09 pm

Hello!

Post by grimmware »

Hey everyone!

I'm grimmware and I've recently been delving into the ZX81 because my dad was getting rid of a bunch of the stuff that he had stored away in the attic - so far I've gotten a ZX81, a Spectrum, an Apple II Europlus (that he had no recollection of ever having seen before) and a Tandy 1400-LT out of him ;)

Combine this with the BBC Micro B, Atari 1040ST, *another* Spectrum and an Amiga 1200 which I'm sitting on because a friend moved continent and left them with me, and the Macintosh that used to belong to my father-in-law and I'm sitting on quite the backlog of old computers requiring care and attention almost entirely by accident!

Anyway, back to the ZX81 - what with these having been so cheap the first time round and the ULA making the design so wholly simple to understand, I've been putting some time and effort in to upcycling it. It had no power supply so I built one out of an old Asus Eee 701 charger, I installed a composite mod and booted it up to find the keyboard membrane didn't work.

Now personally I have a history of RSI so even looking at the keyboard membrane makes my wrists ache, so I decided to take my first foray into PCB design and build an external keyboard for it, which was pretty successful (albeit with some pitfalls). I'll write more extensively about it and share at some point in the future on the appropriate board, but I'm currently trying to figure out the best way to a) dump the ROM as a proof-of-concept (because it's easy to download the ROM or the ROM source but I'd like to achieve this for the posterity of having *my* original ROM) and b) take the listing, modify it (change the font, add some commands) and flash to a new EEPROM.

I love working with the ZX81 - I work as a security engineer and I find a wide range of knowledge really helps in that role, and computers like the ZX81 really help to link that high-level abstract knowledge back to the actual silicon! I also really like the idea of taking old unloved machines that are gathering dust and making them usable in the modern day - my goal with the zeddy is to be able to do some simple note-taking with it, possibly as a battery powered machine.

Looking forward to sharing experiences and getting advice on my builds!
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1024MAK
Posts: 5087
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Location: Looking forward to summer in Somerset, UK...

Re: Hello!

Post by 1024MAK »

Hello and welcome to our forum grimmware!

:D :D :D

I hope you enjoy this forum :D

I’d not heard of the Tandy 1400-LT before, so had to look it up. Apart from the Tandy 1400-LT and all Apple machines (I’m not an Apple fan), I also got the other micros you mentioned :D

As ‘dead’ as a ZX81 membrane is, it’s not as annoying as touch screen ‘keyboards’ (like on modern mobile telephones, tablets and pads).

A ZX81 can run from a battery. Either as is (but you need a big battery for reasonable run times) or If you use modern low power parts (DC-DC converter in place of the 7805, CMOS EEPROM/EPROM, CMOS SRAM, CMOS Z80, and a ULA replacement module) a really great run time from a smaller battery 8-)

The ROM has a slightly different pin-out to the common 27 series EPROM chips. It is possible to construct a simple adapter, insert the ROM into the adapter, then put the adapter into a cheap EPROM programmer. Then you can ‘dump’ the ROM. Or you can use some programming magic to copy the ROM into RAM (assuming you have a 16k RAM pack or equivalent), then save the data from RAM. LOAD it into an emulator, then extract it from there (assuming your chosen emulator can do this (not tried this myself).

BTW are you on another computer forum under that user name?

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
grimmware
Posts: 15
Joined: Thu Feb 04, 2021 1:09 pm

Re: Hello!

Post by grimmware »

1024MAK wrote: Mon Feb 08, 2021 11:29 pm A ZX81 can run from a battery. Either as is (but you need a big battery for reasonable run times) or If you use modern low power parts (DC-DC converter in place of the 7805, CMOS EEPROM/EPROM, CMOS SRAM, CMOS Z80, and a ULA replacement module) a really great run time from a smaller battery 8-)
Heh, yeah looks like that's going to be a slow-burn project if I decide to do much with it - I really just like the idea of being able to type up some thoughts in the garden so possibly something to get 9V off of a USB power bank might do the trick here.
1024MAK wrote: Mon Feb 08, 2021 11:29 pm The ROM has a slightly different pin-out to the common 27 series EPROM chips. It is possible to construct a simple adapter, insert the ROM into the adapter, then put the adapter into a cheap EPROM programmer. Then you can ‘dump’ the ROM. Or you can use some programming magic to copy the ROM into RAM (assuming you have a 16k RAM pack or equivalent), then save the data from RAM. LOAD it into an emulator, then extract it from there (assuming your chosen emulator can do this (not tried this myself).
I've ordered some TMS2532As for this as I read somewhere that they're pin compatible and I found them dirt cheap...

I made the stupid mistake of buying a TL866ii assuming that it would be trivial to reconfigure the thing for any given pin-out only to discover that the thing only supports devices as dictated by what's in the firmware which I've attempted to extract only to find that it has to be decrypted by the bootloader. Another backburner project to see if I can glitch the PIC24 to get it to let me dump the key (I have next to no idea how to do this - yet) ;)

Your suggestion of constructing an adapter for the 27 series is a great idea though - whilst I'm still really interested in a more general-purpose chip flasher that would allow me to get on with what I'm doing whilst I wait for some of the recent crowd-funded devices to come out.
1024MAK wrote: Mon Feb 08, 2021 11:29 pm BTW are you on another computer forum under that user name?
I think I'm on Apple Fritter but I'm not active there and given what you said about not being that in to Apple (me either, all the kit I have I inherited!) I'm guessing that's not where you mean... It's entirely possible it's me - feel free to PM me with the site and I can confirm/deny :P
Lardo Boffin
Posts: 2155
Joined: Sat Nov 26, 2016 2:42 am

Re: Hello!

Post by Lardo Boffin »

Welcome on board!
To be a bit controversial I quite like the Apple II and have a Europlus I am in the process of getting usable. I used to go round a friends house and play Bard’s Tale and Wizardry on one a lifetime ago so its a nostalgia thing. :D
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Moggy
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Re: Hello!

Post by Moggy »

I thought TMS2532As were 4k EPROMs not 8k's, used as replacements for the ZX80 ROM?
Even when used with the 80 they do need a bit of modding.
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grimmware
Posts: 15
Joined: Thu Feb 04, 2021 1:09 pm

Re: Hello!

Post by grimmware »

Moggy wrote: Wed Feb 10, 2021 2:56 pm I thought TMS2532As were 4k EPROMs not 8k's, used as replacements for the ZX80 ROM?
Even when used with the 80 they do need a bit of modding.
It is entirely likely I got the wrong end of the stick when looking for compatibles and bought the wrong thing, but they were a few pounds and would take weeks to arrive so I thought I’d just get on and buy them in case I got distracted ;)

I think I’ll go with the suggestion further up at any rate and keep those chips handy for building something else :)
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1024MAK
Posts: 5087
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Location: Looking forward to summer in Somerset, UK...

Re: Hello!

Post by 1024MAK »

grimmware wrote: Wed Feb 10, 2021 1:52 pm
1024MAK wrote: Mon Feb 08, 2021 11:29 pm BTW are you on another computer forum under that user name?
I think I'm on Apple Fritter but I'm not active there and given what you said about not being that in to Apple (me either, all the kit I have I inherited!) I'm guessing that's not where you mean... It's entirely possible it's me - feel free to PM me with the site and I can confirm/deny :P
Ahh, in that case I must be mistaken. It must be another user with a similar but different user name. One place you definitely will not find me is on Apple Fritter. I have nothing against classic Apple computers. I just don’t have any interest, as I already have too many fingers in too many pies. I use the same user name on all the various classic computer forums that I’m on.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
grimmware
Posts: 15
Joined: Thu Feb 04, 2021 1:09 pm

Re: Hello!

Post by grimmware »

1024MAK wrote: Thu Feb 11, 2021 12:24 am Ahh, in that case I must be mistaken. It must be another user with a similar but different user name. One place you definitely will not find me is on Apple Fritter. I have nothing against classic Apple computers. I just don’t have any interest, as I already have too many fingers in too many pies. I use the same user name on all the various classic computer forums that I’m on.
Turns out I'm a total liar and joined stardot back in April 2020! I probably joined with the intent on seeking some help on debugging some issues with my BBC Micro B and then forgot to actually post anything. I only realised this when clicking through to a stardot link and recognizing your username and then searching my password manager :P
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1024MAK
Posts: 5087
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Hello!

Post by 1024MAK »

No posts :shock: None at all :shock:

Not even a post in the introduce yourself topic :shock:

As a moderator over there (as well as here), me thinks you should at least introduce yourself ;)

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
grimmware
Posts: 15
Joined: Thu Feb 04, 2021 1:09 pm

Re: Hello!

Post by grimmware »

Hahah, yeah I totally should - to be fair I've just got the kit I need to ramp back up on trying to debug why the hell my BBC is so unstable and likes to crap out sometimes.
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