The "Commodore ITX-64"
By Neil Jansen
Posted on April 28, 2003
Jump to:

Internal CRT

A close look at the original SX-64 schematics shows that the video signal is a standard NTSC (or PAL, depending on location) S-VIDEO hookup. Wow, guess what motherboard can give us that signal?! A custom 3-wire cable brings the CHROMA, LUMA, and GND into the CRT.

Now believe me, I don't use this tiny screen on a daily basis. Anything higher than the c64's 40-column mode is unreadable (even the BIOS at 80 columns is too blurry to read), so it remains a novelty, just something cool to look at ;)

Interfacing the Keyboard

The stupid engineers at CBM suck because they didn't make their keyboard PS/2. I realize that PS/2 was not around then, but they could have predicted the future or something! Instead their keyboard is basically a switch matrix consisting of 8 rows and 8 columns. for example, row 4 / column 4 is the "M" key. The circuit above takes the rows and columns, looks up the key in a lookup table, and sends a PS/2 signal out to the motherboard. There are plenty more details about this converter on my site, so check it out.

The other cool part about having a custom keyboard converter, is that I can map my own keys, like the C= key is now the Windows Logo key. I've also added some multimedia keys to adjust the volume and eject the CD media.

That authentic SID sound.....

If the words "Commodore scene" ring a bell at all, then you're probably familiar with the MOS8580 SID chip. This is the king of all synth chips: three voices, four oscillators each, ADSR envelopes, selectable filters and cutoff/resonance, hard sync, ring mod, etc... All in a single chip which is easily interfacable by any microcontroller. You can buy all sorts of (expensive) music equipment that uses this chip, like the SidStation, or the HardSID ISA (and the new PCI version).

Well I have a MIDI keyboard and I want to make some SID music but I just butchered my only SID-generating computer, the SX-64! I don't want to spend $700 on a SidStation, and I don't have a slot for a HardSID. Well I got ahold of the specs, and it doesn't take anything to interface.... So I whipped up a little board complete with an EEPROM lookup table, MIDI in's and out's (which can work without the computer hooked up to it), and a 5-wire parallel port interface (D0-8) to control it from the computer.

The best part of all, Christian from figured out how to emulate a HardSID by using a custom HARDSID.DLL with the same export routines, which means that my new SID2MID circuit can serve as my CCS64 emulator's sound card! Once I'm done writing the firmware and DLL code, I'll be able to hear the authentic C64 music through an authentic SID chip.

CCS64 Emulator

No vintage computer mod can be complete without the matching emulator to bring the project full-circle. My C64 game collection is bigger than it could have ever been with a stock '64.

Completed SX-64 serving as my HTPC

Neil is still tweaking his project! You can find recent updates here...