Root42Tube

Let's Code MS DOS 0x38: Huge Pointers in Turbo C

root42 — Tue, 04 Aug 2026 11:15:49 GMT

In MS DOS you can only access up to one Megabyte of memory easily, on an original PC or XT. This memory in turn is segmented, so accessing more than 64K at a time becomes a bit more tricky. This is why languages like Turbo C and Pascal introduced near and far pointers to the programmer. However there are also huge pointers, which we will investigate in this episode.

Sourcecode: https://codeberg.org/root42/LARGEARR

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Music: A Little Wonder by Spino2006

FPGATED for C16 and Plus4

root42 — Tue, 04 Aug 2026 11:13:39 GMT

The Commodore 264 line of computers included the C116, C16 and Plus/4. They were build around the TED video and I/O chip. Also known as the MOS 7360 and MOS 8360, the early revisions of the chip were plagued with production issues. Many of the early R1 chips are broken by now. Replacements are hard to come by and often expensive. Now there is a modern replacement: The FPGATED by Istvan Hegedus offers high compatibility, together with additional features. HDMI output for modern screens, as well as ROM replacements and SID emulation in future firmware updates. Let's test it and see how compatible it is!

FPGATED project: https://www.fpgated.hu
Config utility: https://plus4world.powweb.com/software/FPGATED_Config_Program

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Music: A Little Wonder by Spino2006

Commodore 4040 Refurb

root42 — Tue, 04 Aug 2026 11:11:07 GMT

Another Commodore 4040 dual floppy disk drive ended up in my hands, but only temporarily for repairs and refurbishing. This drive didn't boot up in the beginning and had other small issues. I will show in great detail how to take these things apart and how to clean them and get them up to speed again.

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Individual Computers C64 Smart Supply

root42 — Tue, 04 Aug 2026 11:07:33 GMT

The old C64 doorstop power supplies and their successors are a bit of a liability if you continue to use them nowadays. The internal voltage regulators like to die, and in the process they can destroy the C64 or worse. There are modern power supplies to replace them, but Individual Computers are now coming out with the "Commodore C64 Smart Supply", including official Commodore branding! And the sales pitch is that this is the best PSU you can get for your vintage C64. Let's take it for a test drive!

iComp PSU analysis (in German): https://forum.icomp.de/index.php?thread/4411-was-macht-ein-gutes-c64-netzteil-aus/

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Music: A Little Wonder by Spino2006

Let's Code MS DOS: 0x37 Rainbow Surf Analysis

root42 — Tue, 04 Aug 2026 11:03:37 GMT

This year's Revision demoparty had a surprising winner in the 256 byte compo. It was Rainbow Surf by Plex/BionFX and it is only 16 bytes long. That is short, very short. In fact, here is the code: c4 04 48 ab 26 03 45 ae 26 03 05 c1 e8 02 eb f2. Let's dissect it!

Demozoo link: https://demozoo.org/productions/389794/
Life 256: https://youtu.be/noNhtyEKeb0?si=00Dr4S2qcV6inS3z

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Music: A Little Wonder by Spino2006

1541 Differences

root42 — Tue, 04 Aug 2026 11:01:32 GMT

The 1541 was the ubiquitous floppy disk drive for the C64. The different drive revisions look very similar, but on the inside there are some significant differences. Not only did they use two different manufacturers for the mechanisms. But the mainboards also had multiple revisions, and one particularly snarky little difference in the 1541C, which was only used on some of the drives that could make swapping parts between old drives very difficult.

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TND232 Tandy Serial Port Soundcard

root42 — Tue, 04 Aug 2026 10:59:27 GMT

The Tandy 1000 and IBM PC Jr utilized the cheap Texas Instriuments SN76489 programmable sound generator. While it never caught on as a sound standard outside of these machines, many DOS games from the 1980s still supported this chip. What if you wanted to listen to video game music using the original chip, no emulation, but you had only a serial or USB port? Well, now there is a solution for you!

Project page: https://www.retroianer.de/index.php/tnd232-serielle-und-usb-sn76489-tandy-soundkarte/
Source: https://github.com/matze79/TND232

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Music: A Little Wonder by Spino2006

Floppy Disk Punch

root42 — Tue, 04 Aug 2026 10:57:16 GMT

Floppy Disk Punch

Back in the 1980s floppy disks were expensive. And many early floppy disk drives were only single sided, which means they only had one read/write head and would only use one disk side. Both Commodore and Apple-II users quickly figured out that you could flip the disk around, if you punched a hole into the other side of the disk. This is a quick explanation on why this helped to double your disk capacity and some other differences between Commodore and IBM disk drives.

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Music: A Little Wonder by Spino2006

Let's Code MS DOS 0x36: Sprites and Occlusion

root42 — Tue, 04 Aug 2026 10:56:19 GMT

In the last video we learned how to make 2D sprites with transparency and scaling. This time around we also make our Guybrush automatically scale with the background, limit his ability to move into nonsensical parts of the scene, and most important: Walk in front and behind objects.

Source Code: https://codeberg.org/root42/VSPRITES/src/branch/feature/mask-and-scaling

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Let's Code MS DOS 0x35: Sprites & Scaling

root42 — Tue, 04 Aug 2026 10:54:25 GMT

Adventure games like Monkey Island utilized sprites that could be moved and scaled arbitrarily on the screen. How does this work on a machine that doesn't have support hardware sprites? We will work our way from simple sprites with no transparency, to ones that are clipped, have transparency and can be scaled down arbitrarily.

Source Code: https://codeberg.org/root42/VSPRITES

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Music: A Little Wonder by Spino2006

Let's Code MS DOS 0x34: VGA Blending

root42 — Tue, 04 Aug 2026 10:50:38 GMT

The VGA card can display up to 256 colors on the screen at the same time, using an indexed 8 bit color mode. This is not much, but it allows us to fade two 16 color images into each other. This looks pretty nifty!

Source Code: https://codeberg.org/root42/VGABLEND

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The OneROM Versatile ROM Emulator

root42 — Tue, 04 Aug 2026 10:49:06 GMT

The old home computers like the C64, PET and VIC20 use a lot of 24 pin ROM chips. Many of those are failing and are often replaced with EPROMs and adapter boards. Those are sometimes hard to acquire, especially for older machines such as the PET. But even more common EPROMs require a dedicated UV eraser, programmer like the Minipro, which all adds up. The OneROM is a versatile replacement for EPROMs based on the RP2350 MCU. It allows for easy reprogramming, multiple ROM images and can replace up to three ROM chips in a single system. Oh, and it's open source!

Piers' channel: https://www.youtube.com/@piers_rocks
Project page: https://onerom.org

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Music: A Little Wonder by Spino2006

Let's Code MS DOS: 0x33 PowerBasic 3D Starfield

root42 — Tue, 04 Aug 2026 10:46:17 GMT

Every year around Christmas we return to the roots. To PowerBasic instead of Turbo C! As Christmas is already over, we do something that is also befitting New Year's Eve: a classic 3D starfield! With some EGA/VGA palette tricks, to make the stars appear smoother!

Source Code: https://codeberg.org/root42/pbstars

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Music: A Little Wonder by Spino2006

Commodore 4040 Disk Drive Repair

root42 — Tue, 04 Aug 2026 10:44:18 GMT

We have another Commodore IEEE-488 dual disk drive. It is the predecessor of the 8050 and it is almost compatible with the 1541, the C64's disk drive. This specimen doesn't work, its drives look quite mangled. So let's fix it! But it is never that easy...

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Music: A Little Wonder by Spino2006

Let's Code MS DOS: 0x32 VGA Split Screen

root42 — Tue, 04 Aug 2026 10:41:54 GMT

A couple of games back in the 1990s utilised the VGA split screen functionality to enable things that were otherwise only possible on more capable machines, like the Amiga. The VGA split screen allowed games such as Jazz Jackrabbit or Pinball Fantasies to display a static status bar at the bottom of the screen, while the rest of the screen was smoothly scrolling in two or more directions. In this video I will show how this is possible, and which VGA registers to program with the appropriate values.

Source Code: https://codeberg.org/root42/vgasplit
CRTC Documentation: http://www.osdever.net/FreeVGA/vga/crtcreg.htm

Commodore SFD-1001 Repair

root42 — Tue, 04 Aug 2026 10:40:10 GMT

Another dead floppy drive has landed on my desk. I was told that "the motor isn't working". That can have different causes, but let's find out what the actual problem is. I never worked on one of these drives before, but they are related to the CBM 8050, a drive that I like very much.

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Music: A Little Wonder by Spino2006

Commodore 1541 Repair: Spin Me Round

root42 — Tue, 04 Aug 2026 10:34:05 GMT

We have another dead 1541 floppy disk drive on the bench today. It is an infinitely spinning drive, so it means that somehow the drive is not booting. But what might be the cause...?

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Music: A Little Wonder by Spino2006

Double Trouble: C64 and 1541 Repair

root42 — Tue, 04 Aug 2026 10:29:32 GMT

I have two dead Commodore devices here, that a user asked me to repair. A 1541 floppy disk drive and a bread bin C64. The drive's motor spins indefinitely and the LEDs don't come on. The C64 has a black screen. So let's get cracking, and repair both! With the C64 I made a couple of wrong turns, but in the end all turned out well! The 1541 had some other idea in store for me, and turned out to be a bit on the spiritual side...

Music: A Little Wonder by Spino2006

The Horror: GameBoy Backlight Mod

root42 — Tue, 04 Aug 2026 10:25:19 GMT

The original GameBoy (DMG) had not the best LCD display that one could wish for. Most importantly it was a reflective only display, which required substantial amounts of external light to be visible. A friend sent me their DMG with the request to install an LED backlight mod. I thought: how hard can it be? Well, you be the judge of it...

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Music: A Little Wonder by Spino2006

Let's Code MS DOS 0x31: ANSI C Data Types

root42 — Tue, 04 Aug 2026 10:21:41 GMT

The C programming language has only few builtin data types. But for a beginner those can be a bit confusing. So we will have a look at what data types are offered, and what kind of new datatypes you can build with C.

Source Code: https://codeberg.org/root42/turboc-types

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Music: A Little Wonder by Spino2006