Posted By
TLC
on 2022-11-11
04:22:06
|  Re: Let's remake the DigiBlaster!
@SukkoPera it looks neat indeed. Re: inverting some signals, I seem to have an idea here. I think the ZN427 datasheet looks to have a typo, I mean it talks about an RD' (RD inverted) output enable strobe on the title page, but later it really shows a positive (non-inverted) one in the read timing diagram. That is, I guess the ZN427 appears to really need a positive read strobe, which seems to justify the need of inverting the cs_adc_r signal.
Also, I noticed that the ZN427 appears to need a clock signal for it's operation, that is, a <= 900kHz one (hint, hint...  ). Ed.: I mean, the hacked-together stable 50% single clock (which the SID card produces to feed the SID with) comes really handy here. It's just within specs. The same construct already wouldn't work in the C64 (or, a standard 985kHz-fed SID) at all.
Yet another comment: I think the 1/2W resistor that you tagged R3 should probably be a small (discrete) inductor instead. I don't know if it really is of course, but... 1.) as you pointed out, the comparator inside the ZN427 needs a negative supply, which (the DC-DC converter, that is) may or may not require an inductor, but more often than not, it does; and 2.) apparently there's nothing in this circuit that'd justify a 1/2W resistor.
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