Using PC Floppy Drives ?

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ChrisO
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Using PC Floppy Drives ?

Post by ChrisO »

I thought I'd got a PC Floppy drive working with my System computer a while ago but that doesn't seem to be the case. Its a Teac FD-55GFR which is an 80 track double sided drive. I've now connected it to my BBC in order to try and figure out whats wrong (8271 floppy disk controller, 2nd 40t drive wired in parallel which works fine).

It will not format a disk, it goes through the motions but on completion the directory hasn't been correctly written to, it seems to be all $E5's ? I've tried the WEDFS FORM40/80 command and a Viglen Utility disk Format.

If I put a preformatted 40t disk in it will read the directory and read and write files as long as they are in track 0, if you go beyond that I get a sector not found error even though the head appears to be stepping out to the right track ?

Any thoughts ?
Kazzie
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Re: Using PC Floppy Drives ?

Post by Kazzie »

Is the Teac just set up as an 80-track only drive, or have you got something double-stepping it when you want to read 40-track discs?

If not, it's quite reasonable for the Teac to only read files from track 0 on a 40-track floppy, as it's the only track that's in the same physical place for both types:

Code: Select all

80t 40t
 0   0
 1
 2   1
 3   
 4   2
...
If you take a disk formatted in your 40-track drive, and re-format in the Teac, what does the catalogue look like when the Teac finishes?

(There are some possible issues with using disks back and forth between 40- and 80-track drives, but that's not worth worrying about at this point.)
BBC Model B 32K issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
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Kazzie
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Re: Using PC Floppy Drives ?

Post by Kazzie »

I've just noticed something else that will cause issues, the GFR version of the Teac FD55 is a 1.2MB, High Density floppy drive. (80-track drives outside the PC world are Quad Density, 40-track are Single/Double Density.)

HD 5 1/4" floppies rotate at a different speed to DD and QD ones, 360rpm instead of 300. If the drive's set up to rotate at 360, when your System/Beeb are expecting it to rotate at 300rpm, then that'll mean the disk finishes a rotation before the computer has finished sending all the track's data to the floppy drive.

From a look at this listing of jumper settings, it seems that jumpers I and IS control the density (and thus the speed) options. The only possibilities are to force 360rpm, or enable dual mode according to the "density select" input.

A PC-standard floppy drive expects a "density select" input on pin 2 of the floppy drive data cable. Pin 2 is unconnected on a BBC Micro (unless you've configured it for 8" drives), so it won't care if you take control of it. (The other drive might misinterpret it though, so try connecting just the one drive at a time to your machine for now.) If you short pins 1 and 2 (effectively grounding pin 2), and fit jumper I (remove IS) that should force the drive to spin at 300rpm at all times, due to a low density select signal.

(I did something similar when using a 1.2MB HD drive with my Beeb some time ago: I used a PC floppy cable with the twist taken out. The edge-connector style connector was attached to the floppy drive, and on the (3 1/2" style) IDC connector I pushed a bridgeing wire into positions 1 and 2.)
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Prime
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Re: Using PC Floppy Drives ?

Post by Prime »

Kazzie wrote:
Sun Apr 14, 2019 7:38 pm
(80-track drives outside the PC world are Quad Density, 40-track are Single/Double Density.)
That may have been how drive / media manufacturers described things but it's slightly misleading.

The single / double density thing is the encoding method of the data, single uses Frequency Modulation (FM) recording and double uses Modified Frequency Modulation (MFM) recording. This effectively affects the number of 256 (or whatever) byte sectors you can fit on a track. So you can have a 40 or 80 single or double density disk.

High desnity disks also use MFM encoding just at a higher clock rate so you get more sectors on a track, you can still physically have a HD disk with 40 tracks, though I don't know any machine that did. Not sure about the encoding used on ED disks :)

So effectively "quad" density was a marketing term where as single, double and high actually describe the density of the data on the disk.

Cheers.

Phill.
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MartinB
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Re: Using PC Floppy Drives ?

Post by MartinB »

If you have a little time, you can read all the Beeb-relevant info and facts behind this HD/DD shenanigans in the HD floppies thread where it even concludes with a little mod circuit that allows the correct (and safe) use of 3.5” and 5.25” HD floppy media (including the use of so-called ‘PC Drives’) with a 177x-based DFS Beeb.... :)
Kazzie
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Re: Using PC Floppy Drives ?

Post by Kazzie »

Prime wrote:
Sun Apr 14, 2019 10:46 pm
So effectively "quad" density was a marketing term where as single, double and high actually describe the density of the data on the disk.
Yeah, I should have made sure to includes some "air quotes" there... :oops:
MartinB wrote:
Sun Apr 14, 2019 11:20 pm
If you have a little time, you can read all the Beeb-relevant info and facts behind this HD/DD shenanigans in the HD floppies thread where it even concludes with a little mod circuit that allows the correct (and safe) use of 3.5” and 5.25” HD floppy media (including the use of so-called ‘PC Drives’) with a 177x-based DFS Beeb.... :)
A good read, especially this post which has some jumper settings for the FD55-GFR.
BBC Model B 32K issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
RiscPC 600 under repair
Acorn System 1 home-made replica
ChrisO
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Re: Using PC Floppy Drives ? (Fixed)

Post by ChrisO »

Thanks all for the replies. Of course you wouldn't expect to be able to read beyond track 0 on a 40T formatted disk on an 80T drive my brain wasn't in gear when I made the original posting !

Anyway I think its fixed thanks to Kazzie's 3rd posting with the link to the image of the jumper settings, I had not spotted the E2 link thats over to the left hand side, fitting that as shown seems to have sorted the problem. Previously format was almost completing but failing with a Drive Fault 10 at 4F/00 prior to writing the directory to track 0, the whole disk was just full of $E5.

The thread on HD/DD is an interesting read but ultimatly my aim is to get this drive (and ideally 3.5" drives) working with an 8271 controller on my System computer, I'm just using the BEEB as a working test bed.

I'll now move the drives back to the System computer and see if they work on there, though I don't have a format command on that machine I can save and load files.

thanks again Kazzie !

Chris
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