Using a separate 6Mhz oscillator wouldn't work because the 6Mhz needs to be frequency and phase locked to the CPU clock which is why the RC oscillator controlled by Phi2 was used in the first place. The only 6Mhz source likely to work is the one on the backplane being generated by the 6502A card as that is already locked to the CPU clock. It's possible that there could be random phase differences on power up with that although looking at the schematic for the 6502A card, the 4,2,1 Mhz clock divider (IC3) is tied to the CLR input of the 12,6,3 Mhz clock divider (IC4) so that might keep the phase relationship stable across power cycles.I once replace IC3 with a 6 MHz oscillator, it fits into the socket and has its output to pin 8. The picture wasn't stable. I tried this because I also want to use my System 5 clone at 2 MHz while using the teletext (VDU 40) board.
There is a discussion of problems associated with the 6Mhz clock that starts here:
viewtopic.php?p=358200#p358200
Statistics: Posted by IanB — Mon Jun 30, 2025 1:53 am