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Old 8th Jul 2019, 2:59 pm   #141
Join Date: Apr 2019
Location: Skipton, North Yorkshire, UK.
Posts: 252
Default Re: Gemini 80-Bus System

I checked the Mux ICs (10, 11, 12, 15, 16, 17) and I can see the negative going pulses on pin 1 in each case.

Turning my attention to the clock, I re-inserted the original ROM and checked pin 6 of IC 3. The clock frequency was 9.38 Mhz and is clearly coming from the VCO as I could adjust the frequency with RV1. Pin 11 of IC 7 was High (6 Low) and as expected given pin 11, no output on pin 10. Just for fun I adjusted the VCO to 16Mhz however, no change.

I will quickly check with the second IVC ROM before coding up a ROM as was suggested by Neal, e.g.
        ld hl, 0xc000           ; status write 
        ld a, 0x02              ; crystal dot clock
        ld (hl), a              ; write
loop:   jr loop
This should give me something concrete to work with.
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