Over Clocking the C64

Date: 2002-10-30 10:13:52

Hi All,

Many know about the trick of switching the PAL 64 to a the NTSC divider and
increasing clock speed to 9/7 times (128%) of the standard speed (screen
scrolls though).

Last night I tried testing for how fast the over-clocking could go by
socketing the 74193 divider on one of the early boards and changing the
value that gets loaded into the counter. I found that 9/5 change worked
(180%), whilst a 9/4 and so on didn't. 

This would suggest the basic components (65xx series) may be rated to 2MHz.
Were the Commodore parts rated to this spec or just that a random sampling
could cope with the higher speed?

I'm not sure as to what stopped working at the higher clock rate... the
board has 120ns RAMs so I guess these are Ok, but.... the board was just
running the standard kernal routine, flashing the cursor at the and when the
system was toggled back to the lower speed some of the characters on the
display were corrupt suggesting a RAM problem? Also cursor had locked up,
but that could be the CIA giving up.... Any thoughts? May be the ROMs?



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