Programming the Commodore 128

One of the most recent additions to my online retro programming IDE is the Commodore 128.

If you weren’t around back when the C128 was released, you might not be aware what an odd duck it was, so I wanted to also share some thoughts about the machine and why I wanted to support it when the C64 platform was already right there …

The C128: Commodore’s Platypus?

Commodore’s 128 is a bit of a weird one. People often forget about it, I know I do (it’s even missing from my retro computer timeline at the time of writing!), even though it was one of my most-wanted additions for my collection.

The reason being, not only is the hardware a weird mashup, but the timing of the thing was strange too.

If you were going to bring out an updated micro, a faster processor is an obvious move. The BBC Micro had a 2mhz 6502 years earlier. Having 128kb of RAM was a normal enough incremental upgrade, several competitors had come out with, or were planning, 128kb machines.

But the C128 wasn’t just a faster C64 with more RAM, they also made the odd decision to target the CP/M business market with an additional microprocessor, a Z80, and an additional video chip and output, allowing two monitors, and 80 column hires (640×200).

Sounds good, right? Well, it is good, and that is why I so badly wanted one. The timing, though, was a different story. This was right at the time when Commodore and Atari were preparing to battle with even more capable 16-bit computers. If the future was going to be 16-bit, and the business world was embracing the IBM PC over CP/M, who was going to notice the Commodore 128?

The popular feeling about the C128 is that most of them were used in C64 mode, which is a shame.

Overlooked Success

Reading the above, you might incorrectly get the idea that the Commodore 128 failed. From its launch in 1985 to the end of production in 1989, it apparently sold up to 5.7 million units worldwide by some estimates, and certainly in the millions. That is massive considering how much competition there was in the world microcomputer market at that time!

Why target the C128?

If you are already comfortable with the C64, you might wonder what the 128 actually gives you as a programmer. You wouldn’t be alone, as most commercial software houses didn’t bother with much in the way of C128-specific versions either.

Here are some things that make it interesting to target in its own right:

• BASIC 7.0 is a nice step up from BASIC 2.0. You get proper graphics and sound commands (GRAPHIC, COLOR, CIRCLE, BOX, DRAW, SOUND, ENVELOPE, PLAY) so you can do things in a few lines that needed pages of POKEs on the C64.
• Structured programming features like DO/LOOP, WHILE, UNTIL, IF/THEN/ELSE blocks and named subroutines make BASIC code much easier to read and maintain.
• 2 megahertz mode roughly doubles the CPU speed of the C64, which is great if you are writing logic-heavy code, compiling on the system, or want snappier BASIC.
• 128kb of RAM split into two banks gives you room to keep code, data, and graphics resident at the same time without juggling.
• The 80-column VDC output is a whole second video chip with its own RAM, ideal for text adventures, dedicated map screens for RPGs, productivity tools, BBS clients, or anything that benefits from more characters on screen.
• Built in Z80 and CP/M mode opens up a completely different software ecosystem if you want to experiment with classic early-80s business software, tools, and languages.
• C64 compatibility with GO64, so targeting the C128 does not mean giving up your existing C64 skills or code, it is more like a superset, and in the IDE, another emulation option …

Commodore 128 in the RGC IDE

Adding the C128 to the IDE also gave me an option to answer some popular enquiries and requests:

• PAL versus NTSC switching – No longer left wondering what screen refresh rate you are seeing
• Full virtual floppy disk read/write support – A blank disk is pre-mounted in drive 8, ready for OPEN and SAVE
• BASIC 7.0 with the C128’s expanded command set (COLOR, CHAR, SCNCLR and friends)
• GO64 support so you can drop into C64 mode straight from your BASIC program
• Lots more granular options (VICE core)

Of course, with any platform in the IDE, I try to offer a wide variety of programming toolchains, and in this first release, I did drop in a set of starter examples, including a CC65 mini dungeon, Kick Assembler colour cycler, ugBASIC keyboard input demo, and a multi-part BASIC tutorial series that goes along with my YouTube videos!