Monday, August 18, 2014

Replacement Clock Generator Chip

I found a fully programmable clock chip that can replace the 8701 and will generate the right frequencies for NTSC and PAL for both the color and dot clocks.  Changing between NTSC and PAL will still require a different fundamental crystal and toggling some DIP switches, but I can place both crystals on the board and have a jumper to select between the two.  Below is my breadboard test with the chip.


  1. Would this get around the need to change the VIC-II chip version when switching between PAL & NTSC?

    Is this something that could be retrofitted to existing C64's?

  2. The clock chip could be wired up to replace the old clock circuit in a C64. It would probably have to be mounted on a PCB with jumpers to control the clocking.

    The VIC chip would still need to be swapped out to match the display since the signal encodings are different between the two. But... I don't see any reason why you couldn't leave an NTSC chip in the board and clock it at PAL freq to match the timings of a PAL demo or other program. The TV or monitor would just need to be able to handle running at the faster frequency.