IDE <-> MFM

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 microcontroller 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 concept. 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. -tony