MODIFY SONY MPF920 DRIVE FOR ATARI USE

General discussions or ideas about hardware.
troed
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Re: MODIFY SONY MPF920 DRIVE FOR ATARI USE

Post by troed » Mon Dec 18, 2017 5:52 pm

exxos wrote:
Mon Dec 18, 2017 3:14 pm
Bikerbob wrote:
Mon Dec 18, 2017 3:09 pm
I suppose a little slower? but so what.. never an issue with wrong write.
I don't understand what you are referring to here..... ?
AFAIK your media change fix indicates media change whenever the drive motor has stopped. That's not the same as what original Atari drives do, so I would also expect "slower" disk reads (as in, TOS would re-read FAT more often) with such a fix compared to using an original drive. It is however perfectly secure against corrupted FAT which is why the fix is a lot better than not having it.

(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 ... )

/Troed

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Re: MODIFY SONY MPF920 DRIVE FOR ATARI USE

Post by exxos » Mon Dec 18, 2017 6:00 pm

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...

EDIT:
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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