Commodore C64 Technical Study

Architecture:

Circuit Diagrams available on the net as scan of hand-drawn circuit.

The Commodore C64 Service Manual is an excellent source of info, and is available on the net.
In fact there is so much information on the net that I shan't bother to gather it on this site.

The C64 is not an easy target, as the parts are quite complex.

Colour carrier modulation

Keyboard (click for details)

Clock circuit

The master timing crystal runs at four times the colour subcarrier of the appropriate TV standard.

14,318,181.81 Base x 4. NTSC master crystal.
 3,579,545.45 Base = NTSC TV colour subcarrier. NTSC master crystal / 4 ?
 1,022,727.72 CPU clock = NTSC master crystal divided by 14.
 8,181,818.18 Pixel clock = CPU clock multiplied by 8

17,734,475.00 Base x 4. PAL master crystal. 
 4,433,618.75 Base = PAL TV colour subcarrier. PAL master crystal / 4
   985,248.61 CPU clock = PAL master crystal divided by 18.
 7,881,988.88 Pixel clock = CPU clock multiplied by 8

The C64 had a link to tell a 74LS163 chip to divide the clock by 14 or 18 for NTSC or PAL crystals respectively.

Jeri Ellsworth's C64 clone

Jeri used to have quite a lot of information about this project on a website, but says it started some flame wars (I don't know why) so has withdrawn it all and plans to just make it public when the whole project is finished. It's very impressive: not only are the original features there, but there are also video co-processors that are more like those of the Atari ST and the Amiga - both 16-bit 68K machines.

Jeri is now in the process of laying out the PCB in an ATX-compliant format, so the end machine should fit into a commonly available PC case.