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mos6502
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6502 posts - new projects and interesting old projects from the archives
6502 posts - new projects and interesting old projects from the archives

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This week, we're visiting the land of Minitel, the game-changing initiative which put an online digital service into every home - every home in France, eventually. And the 6502 was often part of the story, in this case the Computel server running on an Apple II. Indeed, the software, in 6502 assembly language, has been recovered from 30 backup floppies with the help of Floppy Emu and alcohol, and is now on github:
https://github.com/cquest/cristel/blob/master/cristel.a
...
The backup restore adventure, including wrestling with copy protection, is over here, in French:
https://medium.com/@cq94/75837443d7b3

The 6502-based Oric Telestrat even had minitel built in:
https://fr.wikipedia.org/wiki/Oric_Telestrat

indirectly via +Emmanuel Florac on diaspora:
https://pluspora.com/posts/474348
(more 6502-minitel stories and info in that post, and comments)
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This week, Acorn's Atom gets HDMI output and shows it really has 12 colours including three shades of orange. (Generally it's regarded as a 4-colour machine with a choice of two palettes, but it turns out the text and graphics modes have slightly different shades available.) The HDMI output in this case is by means of a Raspberry Pi, with a CPLD middle-end to capture the pixels, and an analogue front end to digitise the Atom's non-binary output levels. The same kinds of techniques might well work with an Amstrad CPC.
...
The original Atom colour board was quite tricky, and there are later and modern designs which do a good job of removing the video-contention noise and producing good levels. The thread is well worth a read! Here's the intro post:
"""I thought I would start a new thread to record my experiences with various Atom colour boards. Since I got my Colour Atom a few weeks ago, I've tried several different ways of getting a proper colour picture:
- The original Acorn colour board that was fitted with an RGB output
- Phill's new design (based on the LMH1251) with an RGB output
- Using Y PA PB on connector PL4 directly as a YPrPb output
- My own design, that I've been playing with this weekend
"""

The RGBtoHDMI project also works wonders for a BBC Micro, as well as for a ZX Spectrum:
https://github.com/hoglet67/RGBtoHDMI/wiki
Other Atom and video projects from the same source:
https://github.com/hoglet67/AtomGodilVideo
https://github.com/hoglet67/AtomVGAWing

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This week, a NES emulation in Emacs (!?!) and therefore a 6502 emulator in Lisp. Almost, but not quite, in 1k lines of code, too. Very much a work in progress and of course not rendering at full speed. (What did you expect?)
...
On lobste.rs we see this comment:
> > I’m not sure if Emacs can really be made to do this kind of thing.
> said no one, ever
gongo/emacs-nes
gongo/emacs-nes
github.com
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This week, a mini-demo of the mini-assembler found inside Woz' monitor inside Apple II Integer Basic.
CALL –151
F666G
You can find reconstructed sources in Jeff Tranter's repo here:
https://github.com/jefftranter/6502/tree/master/asm/Apple%5D%5BMonitor
where we see credits to Steve Wozniak and Allen Baum. But in this oral history it seems the assembler was Baum's work:
"Baum: So it was brute force, very simple and fit into 256 bytes if you already had the 256-byte disassembler."
- https://youtu.be/wN02z1KbFmY?t=3941
Anyhow, one page of code - or two - is very impressive!

For more info, try searching for F666G! (We wonder at this memorable address - the Apple I price was $666.)
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This week, from Micro Technology Unlimited and from 1981, the MTU-130, with an ordinary enough 1MHz 6502, but an extraordinary 18 bit address space. That's 256k, which is to say, 4 banks of 64k.
"When you booted up the MTU-130, the dulcet tones of founder Hal would intone MTU, model 130 in his best wonderful Carolina accent."
...
What's more, the machine had "a custom bus that allowed a 6502, Z80 and 68000 to all share resources." All for $4000 or so, and intended initially as a Digital Audio Workstation, although we read elsewhere that "the stated goal of MTU was to design the top of the line 6502 GENERAL PURPOSE computer system "

The address space expansion is provided by a "unique approach to bank switching—using indirect addressing on the 6502—allows one 64K section of memory to contain a program while the data resides above in its own 64K zone."

There are at least 2 in existence, according to a posting by Paul Hagstrom on the classiccmp mailing list. Many photos:
https://www.dropbox.com/sh/nis5ytxcrc7km9j/AAAe3wMmLwAjYr6j5AgXLjSHa

Ref:
http://www.mtu.com/support/mtuaudioproducts2.htm#1981
http://www.dailykos.com/comments/1013182/43158532#c89

See also the advert in Compute Magazine as seen on the Internet Archive:
https://archive.org/stream/1981-12-compute-magazine/Compute_Issue_019_1981_Dec#page/n71/mode/2up

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This week, a 6502 emulator's unsafe coding of ROM mapping was behind a security flaw on the Linux desktop, back in 2016. Nice to see some 6502 opcodes in a security analysis. Why is the 6502 emulated in a standard Ubuntu installation? So the file manager can preview a Nintendo Sound File, which turns out not to be a sound file as such, more an image of an executable ROM for the 6502-based NES. Be safe out there - write your 6502 emulators with great care!
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This week, the 20MHz all-TTL 6502 rebuild by Drass, which now has its own website, and which took part in a plugathon at the recent World Of Commodore event in Toronto:
"Forum and TPUG member Steve Gray generously volunteered his Commodore PET 8032 for the first test (thank you Steve). Although we'd taken precautions, it was hard to feel absolutely certain the CPU's fast AC logic wouldn't generate overshoots that could damage the PET’s circuitry. After some debate, we decided to go ahead with the test despite the risk that we might have overlooked something. Thankfully, all was well and the PET booted with its familiar jingle-beep and no magic smoke."
Tests with Jeff Laughton's Kim Klone were not so succesful - see the photos and the explanation here:
http://forum.6502.org/viewtopic.php?p=64903#p64903

Drass credits other 6502 forum members ttlworks and Dr Jefyll for assistance and collaboration.
C74-6502 CPU
C74-6502 CPU
c74project.com
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This week, A Visual Defragmenter for the Commodore 64 in just 49 lines of Basic. Mainly for the visuals, as it's pretty slow, and not very full-featured - but feel free to tinker with the source, as the article does a full walk-through and explanation.
https://www.pagetable.com/?p=978
There's even a link to a fragmenter, so the program has something to work on!

[Reposted as a static image - the animated one is too big]
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This week, there's nothing more nostalgic than a fresh build of a 1977 machine - the 6502 based PET from Commodore, of course. It's an example of an early machine that has no custom chips, so can be remade using commodity components. Glen Kleinschmidt has in this case chosen to use all-CMOS parts, for a bit of a modern touch. There's a short video here:
https://www.youtube.com/watch?v=e4uILTKAoj8

Also PET and nostalgia related, Steve Gray's Colour PET upgrade project is worth a look:
http://6502.org/users/sjgray/projects/colourpet We've covered that project before, back in 2013, but were reminded of it by this video on the history of the PET by the 8 bit guy:
https://www.youtube.com/watch?v=eP9y_7it3ZM
(A few things in there we'd like to correct, but it's worth watching.)

Both Glen's and Steve's sites have more projects - be sure to explore!

(The PET clone item is via hackaday:
https://hackaday.com/2018/12/06/a-scratch-built-forgotten-classic-of-the-early-pc-age/
)
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This week in 6502 Emulation, a guide to VICE's debugging facilities - an entry for April's RetroChallenge, from Micah Bly. Might be a nice alternative to real hardware, even with the best machine code monitor ROM.
Other emulators have debug interfaces too: JSBeeb has a simple debugger but also the possibility of digging in with some JavaScript...
https://github.com/mattgodbolt/jsbeeb/wiki/Debugger
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