troed wrote: ↑
Mon Dec 18, 2017 5:52 pm
(And I do remember having read exactly how Atari solved it but apparently not well enough to be able to describe it, will have to search ... )
I don't really know which drive do and do not have media change issues.. Have a Epson 480 I think.. Assume it's a original drive which Atari use... I could investigate that drive...
okay what happens with these drives is WP is pulsed low when the disc is ejected.. The drive does seen to have a detect switch in them internally.
The MPF920 also seems to have a extra switch which does not line up with the density or WP holes either. So there must be some sort of media detect in these drives also, but it does not seem to work same way as Atari drives.
So likely this third switch must trigger a monostable or some sort of one-shot circuit in the floppy controller itself somewhere that it sends a WP pulse, which is then what TOS looks for.
In any case, instead of using the motor on signal as I do on the 1772, the transistor (would need to be NPN in this case ) could be fed from this media detect switch, which I'm just going to call it.. So then WP would be set low when the media change switch is broken (turned off).. This would basically emulate the Atari floppy drive then.
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