I'm trying to extract data from 3.5" floppy disks formatted on a +D interface for a ZX spectrum. It's close but not exactly the same as for a PC. I've written software to do this in the past useing the BIOS to access a floppy.
However some disks are old and have bad sectors. I am trying to create a floppy drive controller to read a disk at a bit level to recover as much data as possible. I'm fully aware of how difficult this might be. I have however written a disk utility program that interfaced with the interface at a machine code level on the original spectrum computer, written in Z80 assembly software to emulate MSDOS to access and write files to FAT12 floppy disks. The original computer that accessed these disks did so using a 3.4MHz processor, so the Rasperry Pi that I'm thinking of using should be more than fast enough. I might even be able to run it from Linux but if not I have figured out to access the GPIO port, screen, keyboard and SD card using assembly language that would not need any kernal to run it. I've read up on how floppy drive reads and write data and have seen some basic example of how to opperate the floppy disk (not just the stepping motor).
I've done some research but have a few questions I can't seem to find answers to, and wonder if people here might know.
1) The read data pin (30). Does this return a logic high/low value of what's under the read head (rounding up or down to logic high or low), or is it analog? I ask because if it's analog, getting any input back would enable me to better try and recover corrupt sectors,but would make interface circuit harder to make, and depending on ADC used make interface with GPIO harder, and slower.
2) I know the molex power of +5V and +12V. But what current would a floppy expect?
3) I assume that the control pins from the ribbon cable on the floppy work at 0 or +5V, but that people seem to be able to run them at +3.3V. Does anyone know what they should be running at, and what their current tolerance are: what voltage and current the inputs expect, and what current/voltage the outputs deliver?
Many thanks for any information/knowledge that you might have on this.
A little late, but if someone else is interested:
1) The data output of the floppy is open-collector. So you can pull it up to your 3.3 Volts and will be fine.
2) 600 mA @ 12V, 500 mA @ 5V should be safe
3) Think of TTL input, that expects 2.4 Volts for HIGH. (2.5V according to the NEC 3.5" floppy drive).