IDE <-> MFM
ard at p850ug1.demon.co.uk
Thu Dec 4 12:54:37 CST 2008
> Chris M wrote:
> > what I had been thinking was shouldn't it be somewhat *easy* to make an IDE
> > drive into an MFM. Just strip off what you don't need!
> ISTR there's still quite a bit of logic on a ST506/412 drive (I think the
> manual's kicking around on Bitsavers and contains schematics) - and I'd assume
There's a fair amount of circuitry, but it's quite simple in fuction, and
splits into several separate blocks. It's basically similar to a floppy
dirve in that you have :
Spindle motor (get the disk turning at the right speed -- unlike a
5.25"/3.5"/3" floppy drive, a hard disk turns all the timem, there's no
motor_on/ signal no the interface connector)
Head positon. On older/simpler drives this is a stepper motor, later ones
ahve a voice coil postioner and have conisderably more complex circuitry.
Often, even in the stepper motor positioned drives this is based round a
Index pulse. On the original ST412, this was a proximity sensor that
detected a magetic 'flag' on the spndle motor, this 'flag' being balanced
by a non-magetic one oposite it.
Write : The normal differential write driver driven from a toggle
flip-flop clocked by the wtite data pin. Proaly some kind of write
current control (either driven from the RWC/ pin on the connector or
automatically from the positioner control circuit)
Head switch. Again similar to a floppy, a diode-based switch
Read : Normal differential read amplifiers followed by a comparator and
the nn a pulse generator.
If you compare the circitry to that of an old-ish floppy drive (TM100 or
similar), you'll see that although the component values change (the hard
drive works at a muuch higher data rate), the circuiry is very similar in
The one dead IDE drive I pulled apart used a voice coil positioner. There
was no separate servo head AFIAK, presumably this thing used an embedded
servo system. Which means you can't write just where you like on the
platter, you mustn't overwrite theservo bursts. Obviously the internal
'IDE' controller enofrces this, but you couldn't simply feed an ST412
type of bitstream to the heads.
As I said, the electronics was built round a few ASICs. It would be very
difficult to modify.
As a more prcatical issue, I thought the idea of this project was to be
able to use a more modern drive with machines that expected an ST412 kind
of interface. If you have to modify the IDE drive, then presumaly it
would only work with that particualr model of IDE drive (and maybe only
one version of it). This hardly seems a Good Thing, I susepct finding the
'right' type of IDE drive (== the one that the original desiger hacked
about iowth to make it have an ST412 interface) would be harder than
finding an ST412.
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