Strange peripherals… the 16-bit Commodore 64

Imagine 3D-graphics running smoothly on a Commodore 64 without any software tricks… Imagine playing a game and have complex graphics scroll without dither across the screen… sounds too good to be true?
Not really, as back in 1987, the C64 community amazed even the hardcore Amiga-fans with a 16-bit powerhouse… and it really still was a C64!

The magic was accomplished by a board, made by a German company called Rossmöller, that you could attach to the expansion port – simple, hassle-free and it even didn’t force you to open up the insides of your trusty C64.

The board basically altered the frequency of your C64 (which normally runs at roughly 1MHz, or 985 KHz to be precise) to anywhere from a complete freeze to about 4 MHz, effectively raising the power of the C64 with 400%!
The ability to bring the C64 to a halt was a nice feature if you were playing a game and were faced with an onslaught of enemies, and you had to take a break from all the action, or just slow them down enough so you could plan your next move carefully J
But of course, the speed increase is the most important, as it really made applications like Vizawrite and Geos shine on the C64.  Gone were the days that when you did a “Find & Replace” in a text, you could go ou for coffee whilst your C64 was slaving away at the task.  Now you couldn’t even see the screen changes with the new speed.

So, what’s the secret of this board that makes all of this possible?  Basically, the board has its own CPU: a 16-bit 65816 processor.
This processor fully emulates the C64’s 6510 processor and takes over the workings of the main CPU whilst in operation.
Next to that, it comes with a CMOS equipped RAM, capable of loading the full 64Kbytes of the C64 in its memory.  Because this memory is battery powered, it allowed for the C64 to be switched of and then switched back on again, with all the programs still running.  Talk about a nice bonus!
It even meant you could run an application, shut down the C64, take out the expansion board, go to a friend, plug it in his or her C64 and continue the application there!

It was further possible to bypass the emulation of the C64 processor and take the full power of the 65816, turning your C64 in a real full-blown 16-bit computer, with a much richer command-set and the ability to address a lot more memory.  It became possible to directly address as much as 16Mbytes of RAM (the same as the Amiga and the Atari ST), with the board having a built-in 1 MByte already.

On the compatibility side of things, the board scored a near perfect 10, with only programs that used the illegal Opcodes of the 6510 showing some issues.

All of these goodies came ready packed for the end-user, without the need to touch the soldering iron.  If you did know your electronics and were not afraid to tinker a bit with the board, the EPROM allowed for 3 additional operating systems to be installed.  It allowed also for the connection of yet another board called the “debugger”, which was a hardware debug-application allowing you to place a stop or step into your machinecode.  Gone would be the days of trying to figure out why that specific interrupt did not work, as you now had the power to go deep into the code and start some professional debugging.

So how much would this 4 MHz board have set you back in the late 80s?  Not too much as the board was on sale for roughly (calculated to today’s Euro) 200 Euro.  A low price as it meant you could really start using your C64 for professional applications and it would guarantee extra years of productive life for your machine as it was definitely on par with the ST’s and PC’s of the time.

It enhanced Commodore’s position as the number 1 computer manufacturer of the 80s with the most popular computer of all time!

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5 Responses to Strange peripherals… the 16-bit Commodore 64

  1. And CMD had their SuperCPU, which was based on the 65816 as well, but running at 20Mhz.

    Great blog :) Keep up the good work!

  2. Robby "The C= guy"

    Thanks for the kind words! Expect more great content this year!

    Indeed, I believe I saw one of these on eBay in November ’10… went > $400…

  3. I believe that when they do appear on, they tend to run ~$1000 USD.

    I just want to get my hands on one so I can try reverse-engineering it ;)

  4. Robby "The C= guy"

    Indeed, that’s the one I saw… very rare items indeed… but still a lot of $$$…

  5. One really obscure bit of commodore hardware that I used was a modem made by a place called BT, or BIT, or BITS Engineering, from Richmond Hill Ontario Canada. It was a 1200 bps auto-answer modem, similar to the Commodore 1650 modem, and I briefly ran a BBS on my commodore 64 using this non-HAYES (no AT-commands) modem. I can’t find anybody on the internet who mentions this company, or this odd little product. It was a hot seller around here, though, back in the day (about 1987).


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