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Jean-Marc Gillet

@duende24.bsky.social
56 followers 62 following 559 posts
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Jean-Marc Gillet @duende24.bsky.social · 10/09/2026
- On the ZX81, both plain and alternate Z80 register sets are freely available to user machine code (with the exception of af,af'). - On the ZX Spectrum, both register sets are available (except af,af' once again) but only in a critical section between di and ei. #z80
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Jean-Marc Gillet @duende24.bsky.social · 16/08/2026
ex (sp),hl is a wonderful Z80 instruction. It lets you end a routine with: ex (sp),hl inc hl ex (sp),hl ret so you can stuff a parameter right after the call without having to clobber a register. I had a eureka moment reinventing the wheel. 🙂 #z80
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Jean-Marc Gillet @duende24.bsky.social · 15/08/2026
You always need some math from time to time. Thanks to the excellent hacker Kerm Martian, we have the TI-84 oriented Cemetech at our disposal. en.wikipedia.org/wiki/TI-84_Plus_series means ... Z80/eZ80 :-) learn.cemetech.net/index.php/Z8...
learn.cemetech.net
z80:Math Routines - Learn @ Cemetech
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Jean-Marc Gillet @duende24.bsky.social · 20/07/2026
Having the ZX81 keyboard image in perfect SVG format was a bit of a Grail to me. I found it ! It is the work Andrivet and you can get it here : github.com/andrivet ZX81-Debugger html/images/zx81_kbd.svg Note: I didn't put an easy link on purpose. It would be too easy to grab without crediting him.
github.com
andrivet - Overview
I do stuff with hardware and software. andrivet has 50 repositories available. Follow their code on GitHub.
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Jean-Marc Gillet @duende24.bsky.social · 27/06/2026
"The ULA will hold the CLK line high when it needs to access the video memory at the same time the Z80 does" www.breakintoprogram.co.uk/hardware/com... Does it mean that the ULA "senses" /MREQ since it is interconnected with the Z80 ? Freeze ! I need video RAM access, not you. Bug off ! 😉
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Jean-Marc Gillet @duende24.bsky.social · 24/06/2026
Barnaby ! 😀
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Jean-Marc Gillet @duende24.bsky.social · 23/06/2026
whereweretheynow.blogspot.com/2023/10/sinc... A very good article about Sinclair by @shammountebank.bsky.social
whereweretheynow.blogspot.com
Sinclair Research
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Reposted by Jean-Marc Gillet
Sham Mountebank @shammountebank.bsky.social · 29/12/2024
whereweretheynow.blogspot.com A blog about tracking down the offices of old UK software houses.
whereweretheynow.blogspot.com
Where Were They Now?
Seeking out Britain's pioneering video games houses.
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Jean-Marc Gillet @duende24.bsky.social · 21/06/2026
A very good use of a dual 6809 8-bit CPU that were powering up the Fairlight CMI IIx sampling synthesizer. (+ an excuse to suggest a great tune from a great composer for a great TV series 🤫 ) www.youtube.com/watch?v=eihm...
youtube.com
Rum Cay
YouTube video by Jan Hammer - Topic
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Jean-Marc Gillet @duende24.bsky.social · 12/06/2026
Great loading screen$ (Wizball - 1987 - Ocean). No obvious colour clash.
Loading screen of the ZX Spectrum port of the game Wizball, carefully drawn to work around colour clashes. A fast green pumpkin-like head at the foreground, as if thrown by a wizard at the back with cyan hat and a red gown. The scene is located on the moon, with a starry black sky. Some pipes lie between the green head and the wizard. A black worried cat on top of a vertical cylinder is looking at the green head.
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Jean-Marc Gillet @duende24.bsky.social · 12/06/2026
The best version of JB's theme is of course the 1977 one, the apogee of disco. youtu.be/PGvk2DXxIGE
youtu.be
Bond 77
YouTube video by Marvin Hamlisch - Topic
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Jean-Marc Gillet @duende24.bsky.social · 11/06/2026
Someone able to do such a demo of Atari VCS quality is a guru for me : Simon Owen tells the making of his Pac-Man. simonowen.com/blog/2012/01... youtu.be/69J3D-XGdlg #Pac-Man #SamCoupe #z80 #sprite
youtu.be
Pac-Man for Sinclair Spectrum (colour)
YouTube video by Simon Owen
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Reposted by Jean-Marc Gillet
The Last Psion | Alex @thelastpsion.com · 31/05/2026
Another cool thing... The Zorkulator! @lockfarm.bsky.social #RetroFest2026
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Jean-Marc Gillet @duende24.bsky.social · 04/06/2026
On the appropriate and good use of #AI, here is an article of superstar Andrew Tridgell (you know, rsync and Samba) relating his experience with #claude . I think that @benjedwards.com will be interested. medium.com/@tridge60/rsync-and-outrage-d9849599e5a0
medium.com
rsync and outrage
I gave up blogging a long time ago (apart from an occasional thing about ArduPilot), I tend to just write code and hope people find it…
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Jean-Marc Gillet @duende24.bsky.social · 03/06/2026
If you play four times and win only once in Ant Attack. PS It isn't a Spectrum, I know, but you got the idea.
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Jean-Marc Gillet @duende24.bsky.social · 28/05/2026
17 years ago, spinning HDs were still a thing. Brendan Gregg was (and still is) a Sun Solaris guru and was monitoring disk latency with his invention DTrace, the ancestor of BPF/eBPF. One day, he was in the DC and ... youtube.com/watch?v=tDac...
youtube.com
Shouting in the Datacenter
YouTube video by Bryan Cantrill
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Jean-Marc Gillet @duende24.bsky.social · 20/05/2026
My own small contribution to Z80 coding. Clean, hand-crafted HTML (download and rename to .html) pastebin.com/EwjgNDaM
pastebin.com
Z80 instructions - Pastebin.com
Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.
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Jean-Marc Gillet @duende24.bsky.social · 17/05/2026
Let's hope that AI won't steer too many people away from IT. We need them to manage AI rigorously and validate what comes from it. www.bbc.com/news/article...
bbc.com
AI could put people off tech jobs and hurt the economy, warns Raspberry Pi boss
Eben Upton warns against claims that Artificial Intelligence will destroy vast numbers of computing roles over the coming years.
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Jean-Marc Gillet @duende24.bsky.social · 16/05/2026
Do you remember n:=(75*(n+1)) mod 65537-1 print n/65536 ? Explanation here www.worldofspectrum.net/ZX81BasicPro...
worldofspectrum.net
Chapter 5: Functions
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Jean-Marc Gillet @duende24.bsky.social · 14/05/2026
That is what I call proper credit to the Agon light firmware author by thebyteattic.com
A closeup of the PCB of TheByteAttic's Agon light Origins edition i.e. an eZ80 based Microcomputer board. The closeup shows not only the product name but also the credit to the firmware author Dean Belfield clearly printed in white.
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Jean-Marc Gillet @duende24.bsky.social · 04/05/2026
Please accept my apologies for a post yesterday about the weakening Gulf Stream. I didn't verify the consequences enough. The *extreme* temperatures will get significantly lower. I was too alarming. A lesson for me. I won't post something on that topic for a long time.
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Jean-Marc Gillet @duende24.bsky.social · 03/05/2026
The humble ZX81 now has style.
A black and white ad for "ZX81 Workstation" in Sinclair User, July 1982.
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Jean-Marc Gillet @duende24.bsky.social · 02/05/2026
Who remembers this strategy game ... without resorting to an image search? I never managed to win a campaign. Wehrmacht reinforcements keep pouring in and surround you.
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Jean-Marc Gillet @duende24.bsky.social · 01/05/2026
The BBC advanced UG describes the neat CRC 256-byte tape block checksum at 16.10 Cassette filing system. It would have been great if the Speccy had put some ROM space aside for a similar technique using e.g. the (anachronistical) CD error corr. algo on 1 KB blocks - en.wikipedia.org/wiki/Cross-i...
en.wikipedia.org
Cross-interleaved Reed–Solomon coding - Wikipedia
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Jean-Marc Gillet @duende24.bsky.social · 25/04/2026
I'd like to have the (informed) opinion of @benjedwards.com on this.
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Jean-Marc Gillet @duende24.bsky.social · 14/01/2026
A good one from Simon Holdsworth, the author of the JavaScript port of EightyOne (usable online) zx81stuff.org.uk/zx81/jtyone.... "For more information about how to use the ZX81, there is an online version of the ZX81 Basic Programming manual" www.worldofspectrum.org/ZX81BasicPro...
zx81stuff.org.uk
JtyOne Online ZX81 Emulator
Play ZX81 games online with the JtyOne ZX81 emulator, with a touch keyboard for iPhone, iPad, Android mobiles and tablets
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Jean-Marc Gillet @duende24.bsky.social · 13/01/2026
There was at least one correct printer for the Spectrum (and the ZX81 but with an adapter): the Seikosha GP-50S www.sinclaircollection.site?page_id=530 I printed many loading screen dumps like this one, the most beautiful coming from Ultimate, of course. Many Z80 assembly listings too...
The Seikosha GP-50S 40-column dot matrix printer (1984) for the ZX Spectrum. It is shown here having printed a dump of the Jet Pac loading screen.
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Reposted by Jean-Marc Gillet
ZXVintage40 @zxvintage40.bsky.social · 04/01/2026
Computer Gamer cover (Feb 1986) #zxspectrum #retrogaming
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Jean-Marc Gillet @duende24.bsky.social · 07/01/2026
Here's a rather original ZX81 emulator written in Perl! It was last updated in 2013. Even if you don't use it, it contains interesting PDF reference documents. github.com/domahony/zx81/ #zx81emu
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Jean-Marc Gillet @duende24.bsky.social · 04/01/2026
I was fond of my Programmer's Hex & Time Calculator in the 80s. Hard to press rubber keys, powered with 2 AA batteries. The back reads "Custom manufactured in Japan for Radio Shack". I wonder if it was Casio.
The Radio Shack Programmer's Hex & Time Calculator EC-4075 and its plastic pouch.
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Jean-Marc Gillet @duende24.bsky.social · 01/01/2026
www.reids4fun.com/566/infinite... m.youtube.com/watch?v=tQwA... At last, a way to have a continuous hello world on the ZX81. 🙂 It's an interesting walk within the ZX Basic internals by Steven. Let's make the ZX81 great again! 😊
reids4fun.com
Infinite Scrolling on the ZX81 with Machine Code Magic
Taking a different approach to scrolling by combining ZX81 BASIc with machine code.
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Jean-Marc Gillet @duende24.bsky.social · 31/12/2025
Could be useful. I'd like to find the same on Z80. github.com/TobyLobster/...
github.com
GitHub - TobyLobster/multiply_test: Comparing 6502 multiply routines
Comparing 6502 multiply routines. Contribute to TobyLobster/multiply_test development by creating an account on GitHub.
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Reposted by Jean-Marc Gillet
More Fun Making It @morefunmakingit.bsky.social · 30/12/2025
I think this could be a big deal in the fight against degrading plastics. There are all kinds of ideas being dreamed up since I told people about this stuff. Can you think of a way it can be used?
youtu.be
Is This the Ultimate Way to Fix Vintage Computer Cases?
YouTube video by More Fun Making It
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Jean-Marc Gillet @duende24.bsky.social · 28/12/2025
@breakintoprogram.co.uk About www.breakintoprogram.co.uk/computers/in... , do you think you would have had the same protocol issue with a FDI chipset (made for USB) such as www.adafruit.com/product/5446 ? I have to interface with old hardware like Sun Fire or HP rp/rx and I'd like to avoid trouble.
breakintoprogram.co.uk
Installing a WCH CH352 PCI serial card on a Linux PC - L Break Into Program, 0:1
I’ve got an old Dell XPS 420 desktop PC that is still in regular use. It runs Ubuntu well enough, and is perfect for retro software development. It does however have one drawback – a lack of legacy po...
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Jean-Marc Gillet @duende24.bsky.social · 23/11/2025
For the sake of reinventing the wheel and partly about #retrocomputing, what would be the best strategy to draw (single pixel width) an ellipse with a given tilt e.g. a 100*200 bounding rectangle rotated by 15 degrees ? I know how to do it the Bresenham way ... but without any rotation.
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Jean-Marc Gillet @duende24.bsky.social · 03/11/2025
@superchartisland.com Durell's (or Clive Townsend's) Saboteur! Maybe an idea for a (un)charted post. Even if I never completed the game, I returned frequently to it to enjoy its design and the sound effects - albeit very limited on the ZX Spectrum. teknamic.com/product/the-...
teknamic.com
The Saboteur! Story - Teknamic Software
In the early eighties, the world of computer games was joined by a curious teenager: Clive Townsend. Talented and hard-working, he created two landmark ZX Spectrum games: Saboteur! and Saboteur II: Av...
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Jean-Marc Gillet @duende24.bsky.social · 03/11/2025
@superchartisland.com You were a bit harsh on Bullfrog's Syndicate. I literally spent hours on it. superchartisland.com/syndicate/
superchartisland.com
Syndicate
Bullfrog/Electronic Arts, Amiga, 1993
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Jean-Marc Gillet @duende24.bsky.social · 25/10/2025
One of the cubes is not in the right place :-)
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Jean-Marc Gillet @duende24.bsky.social · 20/10/2025
I'd rather follow Tux' whereabouts than AF1 these days :-) www.flightaware.com/live/flight/...
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Jean-Marc Gillet @duende24.bsky.social · 11/10/2025
Those were the days...
RQ-SX52D-E305V.90 K56flex
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