Floppy drive interfacing
julesrichardsonuk at yahoo.co.uk
Sun Apr 8 16:41:47 CDT 2007
Philip Pemberton wrote:
> Hi guys,
> I've just dug my not-even-a-tenth-finished floppy disc raw-reader out
> of the cupboard, the plan being to finish it off.
That's weird. That's three of us separately suddenly fiddling with this again
(personally I suddenly stumbled across enough SRAM the other day for a raw,
over-sampled track buffer, which rekindled my interest in actually Getting
> - All I/O lines from the floppy raised to +5V via two 4k7 resistor packs
Hmmm, the SA-400 manual says that the lines should be terminated by 150 ohms
to +5V on the last drive in the chain. Output line 'true' from the drive is
logical zero, 0.0V to 0.4V, 48mA maximum. Output line 'false' is logical one,
+2.5V to +5.25V, 250uA maximum.
Doubtless the manual's available in electronic form somewhere on the 'net -
probably on Bitsavers.
> I can step the head in and out fine, and the motor seems to be spinning
> (the drive's activity light is on at least). What I can't get is any
> form of output from the drive - even /INDEX is stuck floating high
> (FWICT it should pulse once for every revolution of the disc, i.e. about
> once per half-second or so).
300RPM would be a 5Hz pulse rate, 360RPM would be 6Hz, so a bit more than that.
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