4 ms·

How to build your own ZX80/ZX81 (2019)

92 points by elvis70 2y ago

sumanthvepa 2y ago
It was my first computer. We lived in India, and importing it into the country was a huge deal in the 80s. Programming on it felt magical. Even taught my self Z80A assembly language to wring the maximum out of the machine. It determined the trajectory of my career.
- fifticon 2y ago
  I live in denmark, and mirror your comment almost to the word. Especially the idea that programming it felt like doing magic.
- gluecode 2y ago
  Same for me, but with an ATARI 800 XL. I had too many POKEs and PEEKs in my BASIC code. Indian customs took 30 days to release this machine in the 80s.
  - rbanffy 2y ago
    I absolutely love the video chip of the Ataris. The display list approach is nothing short of brilliant, allowing multiple display modes on a single frame.
    - flohofwoe 2y ago
      To be fair, that was also possible on some other 8-bit home computers of the time, but required the CPU to get involved (with tricky timing code to write the hardware registers at the right time). The 8-bit Atari's display list coprocessor is basically the daddy of the Amiga's Copper :)
    - musicale 2y ago
      Display lists date back to the antiquity of computer graphics, and Atari obviously knew how to build game machines. Now we have GPUs which can do all sorts of things, but a graphics coprocessor for an 8-bit machine is a nice addition.
- xcf_seetan 2y ago
  Also my first computer. I got a kit version for half the price. It made me the pioneer of micro computing in my little town, as i was the first to have one. :) I was only 15 years old. Most amazing is that it had 1Kb ram and I had 2 games for it: a chess game and a flight simulator all character based. It was so cool.
- ggambetta 2y ago
  Mine too! I have a picture with my late dad and the ZX81 that has a special place in my heart: https://gabrielgambetta.com/computer-graphics-from-scratch/dedication.html https://gabrielgambetta.com/computer-graphics-from-scratch/d...
  - dcminter 2y ago
    That is an absolutely adorable picture!
  - olddustytrail 2y ago
    Don't sit so close to the screen, it'll ruin your eyes!
    - forinti 2y ago
      I had to get glasses at 48, so it turns out all the warnings were true.
      - ggambetta 2y ago
        I had to get glasses at 17. To be fair, by then I had already spent too much time in front of a screen XD Got LASIK a few years later, and now, 15 years after, still seeing great.
- pkphilip 2y ago
  Same here. I did use the ZX Spectrum in India. Late 80s.
- ghoul2 2y ago
  Whoa. Are you me? Same here. Lived in India, my fathers' friend (based in the UK) gifted him a ZX Spectrum. I was hooked from the day I typed 10 PRINT "myname" on it. Taught myself Z80 assembly, just from the appendix in the Spectrum programmers manual that listed the opcode encodings and mnemonics (mostly just guessing what the opcode did from the mnemonic) - at around 10 years old, I could hand-write and hand-encode the assembly code without needing to lookup the opcode encodings. I was 6 years old at the time. Completely determined the trajectory of my life/career.
rbanffy 2y ago
I had a ZX-81 clone for a few weeks. When my family saw what it could be done, they returned the Prológica CP-200 and got me an Apple II+ clone (still very bare, but it would later gain floppies, 80 column-display, a Z80 coprocessor, extra memory and a modem). I still have that computer and the //e clone that I added later as a second workstation for software development. I did a ton of educational software on Apple IIs.
- klelatti 2y ago
  Out of interest what was it on the ZX81 that impressed your family and convinced them to upgrade?
marktbaldridge 2y ago
I actually did build my own ZX80. http://www.markbaldridge.com/2019/02/vintage-microcomputer-clone-sinclair-zx80/ http://www.markbaldridge.com/2019/02/vintage-microcomputer-c...
buescher 2y ago
Now you just need the vintage "portable" black and white TV set to hook it up to.
jonjacky 2y ago
Also of interest, posted here a couple of years ago: ATX-80 – ZX-80 computer clone with ATmega8 processor https://news.ycombinator.com/item?id=29569523 https://news.ycombinator.com/item?id=29569523 This is not an exact replica like the one linked above, but an ingenious DIY re-creation built with modern parts, including just two ICs, with an ATMega8 processor instead of a Z80. Not an emulation, but a complete rewrite of the original Z80 monitor and BASIC interpreter in AVR assembly.
- musicale 2y ago
  I am reminded of these drop-in replacements for a hardware CPU, implemented in software on the Teensy microcontroller platform: https://microcorelabs.wordpress.com https://microcorelabs.wordpress.com Cycle-accurate emulation with appropriate electrical connections and pinout make it a fully compatible software implementation of the original hardware CPU.
Theodores 2y ago
Great idea in principle, however... In the early 1980's, the ZX81 was the poverty specification machine. Rich kids had their fancy BBC Micro Model B, Atari 800, C64 or other proper machine, in a heated study room, with dependable electricity and other niceties. Working class kids had the ZX Spectrum, Vic 20 or, if their grandma got the memo wrong, something like a Dragon 32 or Oric 1, which counted them out of the games swapping world of the playground. Poor kids had the ZX81 and really poor kids had the ZX81 that you had to make yourself, the kit-form version that was £20 cheaper. Or failing that, a hand-me-down ZX80 or a Microbrain thing with just a hex keypad and a few LEDs. Hence, although it might seem a great idea to make a ZX81 nowadays, for the British poor kid, it comes with the stigma, the reminder that it was you that had the kit-form ZX81, with no heated study room, and no 16K of RAM.
- Scubabear68 2y ago
  We were relatively poor back then. I got a Timex Sinclair 1000 after begging relentlessly for it, $99 was a lot to my dad. I was around 13 or so. Learned BASIC, assembly, a bit of Forth on that thing, and as I grew up branched out to C64 and Apple II’s and PCs, eventually became a professional developer. It all was enabled by the TS 1000 (and by extension the creation of the ZX-80 and ZX-81). To steal a cheesy movie quote, that $99.95 little slab of plastic and chips changed my stars.
- musicale 2y ago
  How is the ZX Spectrum not a great machine? Isn't that where Elite was born? Building a ZX81 from a kit sounds highly educational - not to mention learning how to wring the last bit of performance and functionality out of a tiny system with minimal RAM.
  - Theodores 2y ago
    Elite was Braben and Bell on their Acorn Atom, which became the BBC Micro. Original Elite was tied into BBC Micro specific things such as how the display worked, BBC Elite had a split display mode with black and white high-resolution at the top (Mode zero) and four colour 'mode two' at the bottom, for the 'dashboard'. The AY-3-8912 sound card in the BBC Micro was also part of it. On the Spectrum there was just the beeper, and the display was not capable of those clever modes that Braben/Bell amazed everyone with. I will explain the problem with rutabaga... In northern Europe, nobody wants to eat rutabaga (swede) because that was what people ate when there was nothing else to eat, it was poverty food, best fed to the animals. Actually swede is a fine vegetable, I eat swede all the time, but I never went through a famine. With the kit form ZX81, imagine being an eleven year old in the cold with a soldering iron and a Sinclair kit-form ZX81, knowing that the most you will get out of it is 1K Chess, when your friends are playing JetSet Willy on a Spectrum or better, no need for this wholesome electronics stuff, just mainlining the good stuff, as in games. We were just kidding ourselves about microcomputers and programming, think of your peers and how many of them ever had working code to share with you. It never happened.

92 points by elvis70 2y ago

It was my first computer. We lived in India, and importing it into the country was a huge deal in the 80s. Programming on it felt magical. Even taught my self Z80A assembly language to wring the maximum out of the machine. It determined the trajectory of my career.

fifticon 2y ago
I live in denmark, and mirror your comment almost to the word. Especially the idea that programming it felt like doing magic.
gluecode 2y ago
Same for me, but with an ATARI 800 XL. I had too many POKEs and PEEKs in my BASIC code. Indian customs took 30 days to release this machine in the 80s.
- rbanffy 2y ago
  I absolutely love the video chip of the Ataris. The display list approach is nothing short of brilliant, allowing multiple display modes on a single frame.
  - flohofwoe 2y ago
    To be fair, that was also possible on some other 8-bit home computers of the time, but required the CPU to get involved (with tricky timing code to write the hardware registers at the right time). The 8-bit Atari's display list coprocessor is basically the daddy of the Amiga's Copper :)
  - musicale 2y ago
    Display lists date back to the antiquity of computer graphics, and Atari obviously knew how to build game machines. Now we have GPUs which can do all sorts of things, but a graphics coprocessor for an 8-bit machine is a nice addition.
xcf_seetan 2y ago
Also my first computer. I got a kit version for half the price. It made me the pioneer of micro computing in my little town, as i was the first to have one. :) I was only 15 years old. Most amazing is that it had 1Kb ram and I had 2 games for it: a chess game and a flight simulator all character based. It was so cool.
ggambetta 2y ago
Mine too! I have a picture with my late dad and the ZX81 that has a special place in my heart: https://gabrielgambetta.com/computer-graphics-from-scratch/dedication.html https://gabrielgambetta.com/computer-graphics-from-scratch/d...
- dcminter 2y ago
  That is an absolutely adorable picture!
- olddustytrail 2y ago
  Don't sit so close to the screen, it'll ruin your eyes!
  - forinti 2y ago
    I had to get glasses at 48, so it turns out all the warnings were true.
    - ggambetta 2y ago
      I had to get glasses at 17. To be fair, by then I had already spent too much time in front of a screen XD Got LASIK a few years later, and now, 15 years after, still seeing great.
pkphilip 2y ago
Same here. I did use the ZX Spectrum in India. Late 80s.
ghoul2 2y ago
Whoa. Are you me? Same here. Lived in India, my fathers' friend (based in the UK) gifted him a ZX Spectrum. I was hooked from the day I typed 10 PRINT "myname" on it. Taught myself Z80 assembly, just from the appendix in the Spectrum programmers manual that listed the opcode encodings and mnemonics (mostly just guessing what the opcode did from the mnemonic) - at around 10 years old, I could hand-write and hand-encode the assembly code without needing to lookup the opcode encodings. I was 6 years old at the time. Completely determined the trajectory of my life/career.

rbanffy 2y ago

I had a ZX-81 clone for a few weeks. When my family saw what it could be done, they returned the Prológica CP-200 and got me an Apple II+ clone (still very bare, but it would later gain floppies, 80 column-display, a Z80 coprocessor, extra memory and a modem). I still have that computer and the //e clone that I added later as a second workstation for software development. I did a ton of educational software on Apple IIs.

klelatti 2y ago
Out of interest what was it on the ZX81 that impressed your family and convinced them to upgrade?

marktbaldridge 2y ago

I actually did build my own ZX80. http://www.markbaldridge.com/2019/02/vintage-microcomputer-clone-sinclair-zx80/ http://www.markbaldridge.com/2019/02/vintage-microcomputer-c...

buescher 2y ago

Now you just need the vintage "portable" black and white TV set to hook it up to.

jonjacky 2y ago

Also of interest, posted here a couple of years ago: ATX-80 – ZX-80 computer clone with ATmega8 processor https://news.ycombinator.com/item?id=29569523 https://news.ycombinator.com/item?id=29569523 This is not an exact replica like the one linked above, but an ingenious DIY re-creation built with modern parts, including just two ICs, with an ATMega8 processor instead of a Z80. Not an emulation, but a complete rewrite of the original Z80 monitor and BASIC interpreter in AVR assembly.

musicale 2y ago
I am reminded of these drop-in replacements for a hardware CPU, implemented in software on the Teensy microcontroller platform: https://microcorelabs.wordpress.com https://microcorelabs.wordpress.com Cycle-accurate emulation with appropriate electrical connections and pinout make it a fully compatible software implementation of the original hardware CPU.

Theodores 2y ago

Great idea in principle, however... In the early 1980's, the ZX81 was the poverty specification machine. Rich kids had their fancy BBC Micro Model B, Atari 800, C64 or other proper machine, in a heated study room, with dependable electricity and other niceties. Working class kids had the ZX Spectrum, Vic 20 or, if their grandma got the memo wrong, something like a Dragon 32 or Oric 1, which counted them out of the games swapping world of the playground. Poor kids had the ZX81 and really poor kids had the ZX81 that you had to make yourself, the kit-form version that was £20 cheaper. Or failing that, a hand-me-down ZX80 or a Microbrain thing with just a hex keypad and a few LEDs. Hence, although it might seem a great idea to make a ZX81 nowadays, for the British poor kid, it comes with the stigma, the reminder that it was you that had the kit-form ZX81, with no heated study room, and no 16K of RAM.

Scubabear68 2y ago
We were relatively poor back then. I got a Timex Sinclair 1000 after begging relentlessly for it, $99 was a lot to my dad. I was around 13 or so. Learned BASIC, assembly, a bit of Forth on that thing, and as I grew up branched out to C64 and Apple II’s and PCs, eventually became a professional developer. It all was enabled by the TS 1000 (and by extension the creation of the ZX-80 and ZX-81). To steal a cheesy movie quote, that $99.95 little slab of plastic and chips changed my stars.
musicale 2y ago
How is the ZX Spectrum not a great machine? Isn't that where Elite was born? Building a ZX81 from a kit sounds highly educational - not to mention learning how to wring the last bit of performance and functionality out of a tiny system with minimal RAM.
- Theodores 2y ago
  Elite was Braben and Bell on their Acorn Atom, which became the BBC Micro. Original Elite was tied into BBC Micro specific things such as how the display worked, BBC Elite had a split display mode with black and white high-resolution at the top (Mode zero) and four colour 'mode two' at the bottom, for the 'dashboard'. The AY-3-8912 sound card in the BBC Micro was also part of it. On the Spectrum there was just the beeper, and the display was not capable of those clever modes that Braben/Bell amazed everyone with. I will explain the problem with rutabaga... In northern Europe, nobody wants to eat rutabaga (swede) because that was what people ate when there was nothing else to eat, it was poverty food, best fed to the animals. Actually swede is a fine vegetable, I eat swede all the time, but I never went through a famine. With the kit form ZX81, imagine being an eleven year old in the cold with a soldering iron and a Sinclair kit-form ZX81, knowing that the most you will get out of it is 1K Chess, when your friends are playing JetSet Willy on a Spectrum or better, no need for this wholesome electronics stuff, just mainlining the good stuff, as in games. We were just kidding ourselves about microcomputers and programming, think of your peers and how many of them ever had working code to share with you. It never happened.