The "Commodore ITX-64"
By Neil Jansen - Posted on April 28, 2003
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
catchpole.net 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
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...