[HN Gopher] ZX81plus38 - A ULA-less ZX81 clone
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ZX81plus38 - A ULA-less ZX81 clone
Author : nickt
Score : 57 points
Date : 2022-09-17 15:07 UTC (7 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| denton-scratch wrote:
| ZX80/ZX81 were horribly compromised devices, designed to minimise
| cost based on the components available at the time. I'm not sure
| why someone would want to emulate one (I could understand
| replicating one, I guess). Using modern chips, you can build a
| much more exciting toy for a lot less money.
| rwmj wrote:
| Because why not? What's wrong with doing a totally pointless
| hobby?
|
| BTW there's a decent ZX81 FPGA reimplementation in the MiSTER:
| https://github.com/MiSTer-devel/ZX81_MiSTer
| spzb wrote:
| ZX81 was the first computer I ever used. I learnt to code on
| it. It led me down the path that made me gainfully employed all
| my adult life. It might have been built to a price point but
| that price point meant it could be afforded by my family and
| the rest is history.
| pinewurst wrote:
| Nostalgia takes no prisoners.
| lproven wrote:
| I think because they are simple enough to understand, to design
| and build without pro-level skills, and there's quite a bit of
| software, documentation, and even peripherals out there.
|
| E.g. the Tynemouth Software kits:
|
| https://www.thefuturewas8bit.com/shop/tynemouth-products.htm...
| peterbmarks wrote:
| Took me a bit of research to figure out that ULA is "Uncommitted
| Logic Array"
| rwmj wrote:
| The ZX81 was a ZX80 with all the 74LS chips boiled down to a ULA
| (and the "New ROM"), so in a way this is a ZX80 :-)
|
| (I love these kinds of projects.)
| klelatti wrote:
| Very good point! Didn't the ZX81 add a few things though? It
| had a CPU based video driver driven by interrupts IIRC so the
| screen didn't flash all the time when it was working - very,
| very slow though.
| rwmj wrote:
| I'm not entirely certain. I know you could upgrade the ZX80
| by installing the "New ROM", and I believe that was basically
| just the ZX81 ROM. Not clear if that gave you everything in a
| ZX81 such as SLOW MODE (see other replies).
| johnklos wrote:
| The ZX81 added SLOW mode, which was a big improvement. SLOW
| mode can be added to the ZX80, which is what was done with the
| ZX81plus38.
| dfawcus wrote:
| It was possible to add SLOW mode to the ZX80 with a minor
| circuit addition [1][2], and upgrade 8k ROMs to provide ZX81
| capabilities were available[3][4][5].
|
| [1]
| http://web.archive.org/web/20031006130728/http://home.micros...
|
| [2] https://www.myprius.co.za/ZX80.htm
|
| [3] http://qrp.gr/zx80/romupgrade.htm
|
| [4]
| http://www.fruitcake.plus.com/Sinclair/ZX80/ROMUpgrade/ZX80_...
|
| [5] http://qrp.gr/zx80/romupgrade2.htm
| hvs wrote:
| A similar project has been created to make a ULA-less ZX Spectrum
| 128K: https://github.com/DonSuperfo/Superfo-Harlequin-128
|
| There are a number of 48K clones as well.
| m0llusk wrote:
| > ... I don't remeber ever having a case of covid, but I do
| suffer from the same symptoms. I'm 66 now (2021/2022) so I don't
| see myself getting a job anymore, and consider myself retired.
|
| Really touching to persist with this. Hopefully this work does
| not all suddenly disappear when mortality takes its inevitable
| toll.
| ur-whale wrote:
| What does ULA stand for?
| dboreham wrote:
| Product name for gate array at Ferrari semiconductor.
| christkv wrote:
| Now that is a company that had a wild ride. It could have
| become the Xilinx instead it ended up with a wild story
| involving illegal arms exports and other insane stuff.
| predictsoft wrote:
| Ferranti.
| sveiss wrote:
| Uncommitted Logic Array.
|
| It was a semi-custom chip type, where the silicon layer was
| standardised but the metal layers varied by customer.
|
| https://en.wikipedia.org/wiki/Gate_array
| rwmj wrote:
| Just want to add that they're very common on 1980s computers
| in Britain. Sinclairs and Amstrads have them. And that they
| often fail and are very hard to replace. Essentially you end
| up taking one from another machine, so the stock of working
| machines declines over time.
| aeaa3 wrote:
| Would it be possible to recreate the ULA logic in a modern
| FPGA? And if so, to use it as a direct replacement in an
| original Sinclair/Amstrad?
| johnklos wrote:
| Not only possible, but doable. Not only doable, but
| already done :)
|
| https://www.sellmyretro.com/offer/details/vla81-%3A-a-
| replac...
|
| https://www.sellmyretro.com/offer/details/vla82-%3A-a-
| replac...
| 0x0 wrote:
| Apparently it was a custom chip for the various sinclair
| (zx/spectrum) computers.
|
| *
| http://www.retroisle.com/sinclair/zx81/Technical/Hardware/cu...
| * https://www.bytedelight.com/?page_id=2678 *
| https://spectrumforeveryone.com/technical/zx-spectrum-ula-ty...
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