Also keep in mind the TOD clock interrupt on (one of?) the CIA chips is clocked literally by the AC waveform, so if you have a 60hz AC input to a PAL c64, the TOD clock will run 20% too fast. On 9/19/2018 9:49 AM, Herb Johnson via vcf-midatlantic wrote:
Some of the discussion on this topic, suggests a lack of understanding of the differences between PAL and NTSC. A fundamental difference is: PAL uses 50Hz frame rates (vertical) and NTSC uses 60Hz. Why? It's AC power line frequency: the US uses 60Hz and the UK uses 50Hz. That has consequences.
"Old" TV's in each country have analog circuits which produce vertical scan rates based on AC line frequency. The CRT video display, may see crawling horizontal "hum bars" from magnetically picking up AC line signals at one frequency while displaying another frequency. VCR's run motors and pull tapes, assuming one vertical frequency and not another. And some devices which claim PAL/NTSC compatibility, may more simply run PAL on 50Hz power and NTSC on 60Hz power.
A video device that actually turns PAL signals and PAL frequencies, into NTSC signals and frequencies, would be a somewhat busy design. On the other hand, an LCD TV or monitor - which has no "hum bars" as it doesn't "scan" with a yoke coil, has little analog circuity, doesn't need to depend on the AC line for a frequency reference - can be set for PAL or NTSC and it's done.
Also: if an old PAL computer is run from 60Hz AC power, it may use the AC line as a frequency source (to avoid those hum bars). It's then possible the "PAL" computer will try to produce 60Hz vertical video; but not necessarily PAL horizontal rates - depends on the design.
I don't track these PAL/NTSC issues, or C-64's, but I'm aware of these consequences. That sets my expectations about fixing the problem - I don't expect "a cable" (wires only, not a dongle with a buried processor in it) to solve it. It will be interesting to read about the results on specific equipment. - Herb
-- Jonathan Gevaryahu jgevaryahu@gmail.com jgevaryahu@hotmail.com