Replacing floppy

On a sunny day (Sat, 24 Apr 2010 21:53:36 -0500) it happened "George Jefferson" wrote in :

Yes that should be possible. Floppies consist of cylinders with n sectors on it. Common cylinder numbers are 40, 80, with 8 to 10 sectors per cylinder The interface is serial data line, an an up/down (direction) line, and a step pulse. The step pulse increases or decreases the cylinder number (moves the head in or outwards). Then there is a 'track zero' feedback signal, so the system can calibrate itself. This is all easy to make with a PIC. The serial protocol is either MFM or FM, NRZ code, with CRC added for each sector. there is also a sector number. For writing there is also a write pre-compensation. For reading you will need to regenerate the clock and data from the data stream. Data rate is perhaps 500 kbps, maybe slower. Then there were single sided and double sided floppies, so there is a 'side select signal'. I guess o n 64 MHz PIC perhaps you can bitbang / decode the serial stream, have not tried. A shift register (serial to parallel) would speed up things. Would be interesting project. Maybe use a real floppy controller (8272A ?) and interface that to a PIC. I likely would do it that way. Then with all that work, toss the thing in the trash and buy something modern?

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What model of keyboard is it?

-- Joe

Ah, Musical keyboard. I was initially puzzling over what computer keyboard would have such a need.

How about trying a SmartMedia flash card and one of these -

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Adrian C

This won't work, as it needs drivers installed first. I'm guessing since the FDD is the only data storage interface available, this isn't going to be an option.

On the little reading I've done so far, the situation can get quite complex. There ARE floppy interfaces that supply USB, or CF flash replacement storage devices, however, they are priced quite expensively, from what I've read $500-$1000+ US, depending on features.

Also, I've read one person who had a similar problem with a musical keyboard, where replacing the FDD with a standard PC model did not fix the problem. True, we don't know if the problem wasn't with the disk, however, there WERE various supplies of FDDs that appeared the same on the outside, but the interface was at least a little different.

It would be wise to suggest really cheap options, as it would be rather wasteful on the wallet otherwise.

There are many ways an FDD can be controlled. Older floppy drives usually have many jumpers to accomodate different controllers.

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nico@nctdevpuntnl (punt=.)
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Not NRZ. For both input and output, it's a short (100-300 ns) pulse for each flux transition. For the input, inside the drive it's the clock for a T flip-flop that (gated by the enables) drives the head. For output, it's a one-shot triggered by a peak detector.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

If you want it read-only, fed by flash, it wouldn't be too hard. A couple of outputs to fake the drive signals (index, track 0, etc). Inputs for step, direction, drive enable, motor on, etc. The datastream is documented in the floppy interface chip datasheet, or there are various ISO standards for floppy formats that tell you enough information.

The main problem may be in reading in your original so you can save it to flash. I suspect this may be one of those rare 3 inch Hitachi hard shell diskettes. Few folks used them. Roland keyboards and the Amstrad computers. (Sony won that battle with their higher capacity

3.5 inch diskettes). As I remember, electrically, the 3 inch drives were the same as a double density (360kbyte) 5.25 drive.

There is (or was) a web site for a guy in Silicon Valley who had a unit where you can replace the floppy drive (for various classic home compters) and up and download floppy images from a PC. Search for "Semi-Virtual Diskette" or "SVD".

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

On a sunny day (Sun, 25 Apr 2010 18:27:31 GMT) it happened snipped-for-privacy@eskimo.com (Mark Zenier) wrote in :

I think you are wrong:

As is standard when discussing hard drive encoding schemes, MFM encoding produces a bit stream which is NRZI encoded when written to disk. A 1 bit represents a magnetic transition, and a 0 bit no transition.

I should know, I designed a multi standard floppy controller board, and it works :-) It has one of the lowest error rates in the universe, ZERO. Want the diagram?

I would like to replace the floppy interface in a TDS3034 DPO with some USB or Ethernet interface.

Emulating a floppy is a possible method?

Would a PIC chip do that? Hang off the floppy drive cable, intercept and interpret the signals? Make the DPO think it's talking to a real floppy disk?

Grant.

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Thanks.

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On a sunny day (Tue, 27 Apr 2010 09:04:49 +1000) it happened Grant wrote in :

If you ask me outright 'can a PIC do that?', that would take a lot of investigation. Much simpler is in my view to use one of the many dedicated floppy controler chips *together with* a PIC. I used the 8272A in the past (same as in the IBM PC).

If you boot from an SSD, it appears as drive A: on some Motherboarss, and drive C:" on others, and still others allow selection in the MOBO BIOS as to how it gets treated.

No. Just get the USB multi card reader. I installed Vista and W7 from a mem stick onto a Revo, which has no floppy.

Also, if you boot DOS on a mem stick, it usually definitely shows up as drive A:

The data rate on a floppy interface bus is too slow, even if the 2.88MB choice is used.

Chimes in Jan, with yet more guess as you go stupidity.

If it doesn't cover 2.88, it ain't worth a shit.

The data rate on the bus is too slow. Dump the idea.

At least you are smart enough to know that it is not possible on the floppy bus.

Set your clock right, dingledorf.

This is what you need :)

Etc. etc..

Have fun..

RTFDS, I suggest one of the Western Digital floppy controller ones like the 279x family. Or the MC3469, '70, '71 floppy drive electronics ICs.

Er, you see the phrase "when written to the disk". Go look at an old floppy drive schematic. (There's one in the original IBM PC Hardware book, if you're as big a packrat as I am, or I could scan some others that I have). You'll find that the write data line is used to clock a T flip-flop, so what's in the cable is not what's on the disk.

Check and see if you've got a RC and Xor edge detector on the write data line...

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Wrong end of floppy cable :) I want to emulate the floppy end of the cable.

Grant.

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