99.8% Compatible? The C64 Mode of the Commodore 128

The Commodore 128 has a highly accurate Commodore 64 mode built into it. Because of the huge games library for the C64, some C128s spent most of their time in C64 mode despite all the "real computer" advantages the C128 mode has. But C64 mode on the C128 is not perfect and some games will not work on it. In this video we'll show several examples, and where possible, provide explanations and fixes for the failures.

To support 8-Bit Show And Tell:

Index:
0:00 Intro: 99.8% compatible?
2:48 Location $D030 - POKE 53296,1 - FAST
5:27 Scrolls of Abadon on C64 and 128
7:54 Fixing Scrolls
10:24 Cohen's Towers on the C64
13:02 Cohen's on the C128 - Fixing
14:37 Wanted! Monty Mole on 64 and 128
16:55 Fixing Monty Mole
19:16 He-Man Ilearth Stone on 64 and 128
21:26 Fixing Masters of the Universe
26:14 Frantic Freddie on C64
28:15 Freddie on 128 - $D5xx sound fix
34:18 A bit of info from Kris Hatelid - developer
35:47 Another SID mirror example in BASIC on 64 and 128
38:20 Location 1 difference - cassette example
42:23 More location 1 - CAPS LOCK - Cassette Play button
46:16 1571 Problems?
48:45 Gemstone Warrior v1.1
51:22 Autoduel & Moebius fail on 1571
52:53 Autoduel & Moebius work on 1541
56:51 A bit more info...
58:34 In Conclusion - and thanks!

[LeftoverBeefcake]

The command to kick the 1571 into double-sided mode on the C64 is OPEN 15, 8, 15, "U0>M1":CLOSE 15 and to go back to single-sided mode substitute "U0>M0" instead. I made a little cheat sheet of disk commands when I first got my 1571 off eBay a few years ago. It's so nice to have 1328 blocks of space compared to the usual 664 without having to flip the disk. ;)

[scottfromderby]

Loved this! I like to imagine Robin is effortlessly just finding these solutions and fixes during the video without all the hard work and hours of research :P

[JohnnyWednesday]

Given some of these may never have been patched by anybody - you probably now hold a speed-running record for the C128!

[allenhalsted]

1:48 made me nostalgic for the golden days when flipping through someone else’s collection of floppy disks was a journey filled with excitement and wonder! Every disk held the promise of a new adventure, a game never played, or a program never used. The words on each label teased endless possibilities, sparking imagination and curiosity. Ah, those were the days when discoveries were made not through a search bar but through a tangible, colorful stack of potential fun and learning!

[daf]

56:34 You should send them back to Origin, and they will send you a replacement.

[chrismason]

Everyone. Please start sharing robins page with everyone. He doesn’t have near enough the YouTube subscribers that he should. He should at least be in the 500 k range so help him out

[BasicBitesCA]

Great research and testing! On the topic of 1571 problems at around 48:00 -- in addition to knowing the exact version of software being tested, it would be equally valuable to know whether the drive used for testing contained the 03 (initial) ROM or the 05 (fixed) ROM, as it has been suggested that they may differ in 1541 compatibility. -- JC

[DavidYoud]

@36:07 Nice, you're treating the SID like a 1-bit speaker, and in BASIC no less. Very cool!

[stefanjohansson]

Educational, interesting and great without being boring! As always! Thanks Robin!

[Zadkiel]

The reason you weren't able to find any software that breaks because of the bit differences in address 1 is because it would be programmatically a bad idea to check against the whole byte value when you are only checking for the state of individual bits. You can't control the other bits nor do you want to check them, so the 'correct' thing to do would be to take the value of byte 1 and then AND it against the correct bitmask to check the bits you want. And if programmers did it that way, then it wouldn't be affected by a different bit changing.

[shadesofbeige]

Thanks for your tireless efforts while researching this video. Fantastic work as always my friend. 👍👍

[PXAbstraction]

OMG COHEN'S TOWERS! I had this game on my Atari 130XE back in the day and I couldn't for the life of me remember what it was called. I've spent literally years trying to remember. Thanks again Robin! 🙂

[technicalViking]

OMG! The Run Magazine Cover at 1:35! I wrote Address Box 128 when I was 16 years old. I have not seen this cover in literallty 35 Years! Thank you for making my day!

[vintagetechnologies]

Hi Robin, nice video!
At the end it's not the C128 to be not fully compatibile with the C64, the truth is that some C64 software are buggy but they still run on the actual C64 because it has less registers than the C128, expecially for the VIC II, and so as result it's more tollerant to these bugs types.

[andrewgillham]

If we believe Google saying there have been 5, 000 - 10, 000 games released for the C64… That 99.8% compatibility should translate to about 10-20 incompatible games. I don’t know. Sounds like it is closer to 99.9% compatible based on your research. 😀

Great video Robin. I was actually expecting a few more incompatible games based on the anecdotal hearsay about the C128 / 1571 I’ve heard/read over the years. Nice to see the results of all your research and how even the “confirmed list” isn’t all that confirmed without identification of specific versions.

[Lofote]

The reason, why $D500 doesn't mirror SID anymore on the C128, is because it was used there for other chips:
$D500+= MMC of C128 (not accessible in C64 mode, but it also means it doesn't mirror to SID in C64 mode)
$D600+= VDC 80col mode of C128 (actually also accessible in C64 mode)

[daw]

He-man was the only game I came across that did not work back in the day. I remember feeling annoyed that my friends could play it but not me. 🙂

[timpsensky]

lol, the spreadsheet at the end shows the last V8 by Matertronic.... Did they predict the cars movies franchise 20 years earlier? We may never know...

[mechaform]

Outstanding compilation of discoveries and diagnostics! I wouldn’t be surprised if you pushed compatibility up an extra 0.1% for a 99.9% Frantic Freddy rules; that music brought back good memories!

[GadgetUK]

Brilliant video Robin!!! =D I suspect the cassette version of Gryzor may "work" using that capslock test btw! That has a check to determine if the tape is playing still - as it ends loading. (basically its to check you didnt dump it and run from FDD...)