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Old 12th Jan 2015, 11:21 am   #1
AlanC
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Default BBC Model B disk drives

Hi all,

I have a BBC Model B with Issue 3 motherboard, 8271 disk controller in the IC78 position and DFS 1.92.

Am I right in saying that this is not in any way compatible with a 'modern' 3.5 inch floppy drive a la PC variety?

Cheers
Alan
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Old 12th Jan 2015, 12:32 pm   #2
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Default Re: BBC Model B disk drives

The circuits supporting the 8271 in the BBC Model B don't cope well with the lack of an index pulse after stepping the head on 3.5" drives, resulting in 'drive not ready' errors when reading larger files. Or at least, that's how I understand it. There exist patched versions of DFS (V1.21) which ignore the resulting timeout error and can therefore work, but even though I've installed one in my BBC I haven't tried it with a 3.5" drive. It's probably worth a try though.

I don't recognise a DFS version 1.92, though - who made it?#

Incidentally, do you want to use a 3.5" drive simply because they're more common, or do you want to read other BBC 3.5" discs? In my experience most 3.5" BBC discs were formatted double density ADFS, which your 8271 has no chance of reading. If you just want a disc drive and don't care about reading other peoples' ADFS discs, you should be OK.

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Old 12th Jan 2015, 1:16 pm   #3
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Default Re: BBC Model B disk drives

Hi Chris, and thanks for replying

The DFS version may be wrong- I did a *HELP at home (at work now) and that's how I remembered it but could of course be wrong!

It's Acorn DFS.

I wanted to see if this will work with a 3.5in floppy drive purely because the media are more readily obtainable. I don't need to read any other disks.

When I acquired the computer it had the power cable and ribbon cable with edge-style connector for a 5.25in drive, but it came without a drive.

I have a PC-type 5.25 in drive; but no disks. However, when I connect the drive up, I can do shift-break or *CAT and the drive light comes on and the motor runs.

I also have a 3.5in 1.44Mb drive, and when I connect that using a different cable (the type you use in a PC), nothing happens at all- it's as if the drive were not connected. So I hunted around and found a cable that has connectors for one 5.25in drive midway along it, and a 3.5in drive at the far end; with the twisted section in between for drives A and B on a PC.

The 5.25in drive works as expected on this cable, but again the 3.5in drive does not- not light, no motor, no nothing.

Next I straightened out the twist in the cable and tried again; thinking that this would give both connectors the same address, but with the same results.

For the power for the 3.5in drive, I have made up an adaptor from an old power supply cable to power it from the bigger 4 pin plug on the end of the BBC's cable, and that works okay; the voltages measure near enough at the drive- 4.8v and 13.7v. Looking at the PC board though the 12v pin isn't connected so it looks like this particular drive only needs 5v.

Logically, the drive could of course be faulty- I should try it in a PC I guess just to eliminate that element. It came out of a case that hasn't been run up for 10 years probably, but AFAIK it did work.

So that's where I am! Any thoughts welcome!
Cheers, Alan
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Old 12th Jan 2015, 1:43 pm   #4
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Default Re: BBC Model B disk drives

Not sure how well a 1.44HD floppy will work although some you can downgrade to 720K by moving a jumper, I know playing with my Amstrad CPC6128 I could get it to work fine with an old 720K pc floppy drive but had to do some mods to a 1.44mb floppy before it would work. also what position is drive select set to on the floppy? pc's I think used DS1 and used the twist in the cable to identify the drives. The BBC will be expecting the drive to be set to DS0, its usually selectable on a pad or jumper.
Ps if you want to play with your 5.25" drive I have lots of used 5.25" disks and would be happy to let you have a box, I'm only over the hill from you.

Jay
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Old 12th Jan 2015, 1:45 pm   #5
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Default Re: BBC Model B disk drives

Try an old Amiga or ST internal drive, They are DSDD but also there was something specific that was that you couldn't use a PC one in an amiga without mods, not just the fact it was HD. You will definately need a 1770 instead of the 8271 though.
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Old 12th Jan 2015, 2:11 pm   #6
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Default Re: BBC Model B disk drives

Jay you might have hit the nail on the head with the drive select- on this drive, there looks to be 4 solder pads adjacent to the ribbon cable pins, there are no jumpers as such. I'll have a closer look tonight. Thanks for the kind offer, might eventually need to take you up on that!
Alan
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Old 12th Jan 2015, 2:12 pm   #7
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Default Re: BBC Model B disk drives

Courtney_Louise thanks for the info
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Old 12th Jan 2015, 3:03 pm   #8
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Default Re: BBC Model B disk drives

Floppy drives for use in PCs are set to DS1 by default and rely on the cable twist to do the drive selection. The BBC expects the drive select jumpers to be set correctly for each drive.

A quick test would be to connect the drive to the Beeb by a straight cable and try

*.1

to access drive 1. That should get the drive to light up. If so, it should be a simple matter to change the drive select jumper on the drive. Bear in mind that I've seen some late production 3.5" drives which don't have any drive select jumpers - they're just hard-wired to drive 1. That's not helpful, but probably fixable with a bit of track cutting. Your row of solder pads sounds promising, though.

Good luck!
Chris
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Old 12th Jan 2015, 4:47 pm   #9
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Default Re: BBC Model B disk drives

Good advice from everyone above. Your DFS version is probably either 0.9 or 1.2. Version 0.9 had a few major bugs in it, but it will get you going. However, version 1.2 is much better.

I am a little concerned about the lack of life from the drive, I would have expected the motor to spin up when any drive is selected. In a dual-drive setup, when one drive is accessed, the motors of both drives spin up regardless of which is actually needed. As has been said, you will need to change a jumper to get the drive to work in 720k mode. Some do not do this. Have a search on Google for your model number.

I use a 720k 3.5" and 800k (Beeb size) 5 1/4" drive together on my main model B, using the 8271 without any trouble. Perhaps I am just lucky with my choice of drive.

If you get a drive going, you may want to make links 3 and 4 on the keyboard (counting from left) to reduce the step time of the drive's head motor. This makes for much faster and quieter operation. All but the very oldest double-height 5 1/4 drives can handle the speed.

Mark.
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Old 12th Jan 2015, 7:00 pm   #10
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Default Re: BBC Model B disk drives

I understand that many later 3.5" floppy drives will not work with 720k disks. I wasn't aware of the possibility of changing the disk type by jumper selection. A few years ago I bought an external USB-connected 3.5" floppy drive from Maplin that said on the box that it was suitable for both 720k and 1.44M disks, but it wasn't, and I got a refund. When using that drive, 720k disks were not recognised and the disk format menu had no 720k option. Fortunately the IT department at my wife's school dug out a redundant Dell USB external drive that could read and write both types. I only needed it to transfer files from my Amstrad PCW that had been made on its 3.5" 720k external drive and than wipe the disks.
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Old 12th Jan 2015, 8:54 pm   #11
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Default Re: BBC Model B disk drives

Wow, all very useful information, thank you. Firstly, the DFS is 0.9. My mistake. With the 3.5in drive, if you do *.1 the light comes on and the motor runs- yay! Now; the drive is a Panasonic JU-257A606PC which, judging from the wealth of into the net, must have been quite common. It doesn't have jumpers, but it does have solder pads and I found an article here that details how to select Drive 0 (and other things, for the Amiga). So I can do that; albeit the pads are incredibly small and to get to them requires disassembly including desoldering a ribbon cable. But I'm happy to have a go!

The next problem is; with drive 1selected, presumably because the format on a PC formatted disk is not valid; the beeb just sits there waiting to read something. It doesn't seem to time out, or perhaps I just haven't left it long enough. But just assuming for the moment that this is normal, the next question is, how can I get a disk formatted for the beeb?

For info, the other jumpers on the Panasonic drive are marked MS - MO, RY - DC, and PC-AT-P2-SE.
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Old 12th Jan 2015, 9:12 pm   #12
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Default Re: BBC Model B disk drives

Alan,

You should, eventually, get Disc Fault 18 at :01/00 if you are using drive 1. This is a good error to get, believe it or not, as it means everything else is well and the Beeb just can't find the first sector on the disc in drive 1.

Now for formatting. The short answer is - you can't. DFS 0.9 and 1.2 had no built in formatting commands, you had to load the formatting programme from a disc. Later DFSs had the format command where it should have been in the first place, on the ROM. However, this doesn't help you. I could send you a disc with the format prog written on it if this would help you. The other option would be to scan the internet for a sound file of the programme which you could then play through the sound output of your PC and into the cassette input of the Beeb. Or you could type the listing in manually, if you can find a copy out there .

Some utility ROMs such as Disc Doctor, a useful set of tools, had a format programme included. I could programme a ROM for you, if you have any sockets free inside your Beeb.

Let us know how you get on and if you need a disc or a ROM.

Mark.
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Old 12th Jan 2015, 9:14 pm   #13
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Default Re: BBC Model B disk drives

Do you have a *FORMAT command as part of the disc support software?

I don't think this came as part of the standard software package, but was included in a number of auxiliary disc support packages.

EDIT: As usual, someone else manages to post while I'm editing and checking.
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Old 12th Jan 2015, 9:16 pm   #14
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Default Re: BBC Model B disk drives

A quick scan with Google revealed this listing which is a lot shorter than I thought it would be, plenty short enough for typing in. Give it a try.

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Old 13th Jan 2015, 9:36 pm   #15
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Default Re: BBC Model B disk drives

Thanks Mark for all your kind offers of help, and others too. I do have a spare ROM socket in the Beeb and that option sounds rather attractive! I'll pm you regarding that if I don't have any joy with the listing. First thing though is to get the drive jumpered to be drive 0.

Great fun playing with the beeb, easy to forget just how sophisticated a machine it was for its time. For me (I write software for a living) one of the best features is the superb 6502 assembler, and being able to write assembly language instructions inline and mix them with BASIC.
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