Add switch to dual drives to allow booting from either/or?

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colwilliamsnz
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Add switch to dual drives to allow booting from either/or?

Post by colwilliamsnz » Sun Apr 28, 2019 6:35 am

Per subject. I recently renovated a nice stacked double disk unit for my Beeb model B and have installed 3.5" and 5.25" drives. I'd love to be able to add a switch to the rear of the enclosure to allow me to change the logical 0/1 disks for alternate booting. Is this easily doable?

Cheers.

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AndyF
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Re: Add switch to dual drives to allow booting from either/or?

Post by AndyF » Sun Apr 28, 2019 7:10 am

I'd assume here that it would just be a case of a DPDT switch to move the 'DS' between each drive to do this, the same way you'd have to manually mod a modern (ish) PC 3.5 DS link to make it work as DS0 (where possible) although before anyone else replies with more info to hand it *might* be slightly relevant if we know which is set as 0. :)

By that I mean is 'drive 0' currently the 5.25 or the 3.5 ? I nearly asked you which types you had :lol: until I re-read your question and you said you'd got one of each! :D

It might not be need with a DPDT switch but my 'method' would to be to not play with the cable and simply extend the three wires out from each drive if possible so that you could link the 'input to DS0 or DS1' and when the switch was the other way it would be swapped over, then repeat this for the three wires for the other drive, but the other way around so that when DS1 was linked on 'second drive' , DS0 was linked on 'first drive' , I can see it in my head and how that would work.

I'd hold off my idea until someone else posts though as although it would work (honest) someone else may suggest an easier method.
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Re: Add switch to dual drives to allow booting from either/or?

Post by colwilliamsnz » Sun Apr 28, 2019 7:28 am

Hi Andy, the 3.5" drive is currently drive 0.

To be fair, I'd probably add a Gotech unit in place of the 5.25" simply because I struggle to find media for it that actually work reliably (old disks are fine but have been copied to 3.5 now).

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Re: Add switch to dual drives to allow booting from either/or?

Post by AndyF » Sun Apr 28, 2019 7:47 am

colwilliamsnz wrote:
Sun Apr 28, 2019 7:28 am
Hi Andy, the 3.5" drive is currently drive 0.

To be fair, I'd probably add a Gotech unit in place of the 5.25" simply because I struggle to find media for it that actually work reliably (old disks are fine but have been copied to 3.5 now).
:) Greets.

That does make some sense. I no longer have a working 5.25 although I've only got a couple of discs in that size now and they have been preserved, one was the ViewData one (Thanks FlaxCottage for his assistance with this, top chap he is) , so what you're saying does make perfect sense. IIRC the other is an original L3 FS disc which is slightly pointless as its got the dongle protection on it obviously and I've got a very dead clock unit.

Although I'm aware of a GoTek and Mark (Retroclinic) amongst others sells these I'd await others inputs on this for now. I think he might have some up listed on a certain auction site etc but I've no personal experience of the 'modern replacements' for them so as I say I'd simply wait a little bit for others to chime in with their thoughts on this. The GoTek units from viewing them on YouTube and the like do seem a good way to go however, it is quite likely one will be on this years Xmas list for myself.
Last edited by AndyF on Sun Apr 28, 2019 7:47 am, edited 1 time in total.
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Re: Add switch to dual drives to allow booting from either/or?

Post by tricky » Sun Apr 28, 2019 7:54 am

Just an idea, but as well as adding a switch two swap the two select lines you could add a second one two swap between the 5 1/4 and a gotek.
Is there any reason you can't drive three drives in parallel apart from the beeb only connecting two of the three select lines?

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Re: Add switch to dual drives to allow booting from either/or?

Post by colwilliamsnz » Sun Apr 28, 2019 8:08 am

No reason except I like the idea of a nice tidy two drive enclosure ;) maybe I'll retain the 5.25" to keep it more real :)

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Re: Add switch to dual drives to allow booting from either/or?

Post by cmorley » Sun Apr 28, 2019 8:17 am

@AndyF Goteks are only £12 delivered from eBay and it is a simple hobby project to add the rotary control and text display.

Since 3.5" drives are half the height of a 5.25" drive with a double drive 3.5" to 5.25" adapter then you can fit all three (3.5" floppy, 5.25" floppy, 3.5" gotek) all in the existing enclosure nice and tidily. I think that is what Tricky is suggesting.

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Re: Add switch to dual drives to allow booting from either/or?

Post by flaxcottage » Sun Apr 28, 2019 8:19 am

This is actually dead easy to do.

You will need a 4-pole 2-way switch to swap the arrangement of wires 10 and 12 in the floppy cable. These are responsible for the drive select. The aim is to switch each drive between (10-10 and 12-12) and (10-12 and 12-10) configuration. Whilst one drive is (10-10 and 12-12) the other is (10-12 and 12-10).

I'll draw up a circuit and post it a bit later. :D
Drive switching.png
The cable into the dual drive system has lines 10 and 12 cut. These wires connect to the Input lines in the diagram above. The cables going to each drive (A and B) have their 10 and 12 wires connected to the other side of the switches as shown. The cable should be a straight cable with no twisted wires 10-11-12.

Defo works because I used this yesterday at the WROCC show to join a GOTEK and a 5.25" drive and swap drive numbers. :D
Last edited by flaxcottage on Sun Apr 28, 2019 8:52 am, edited 2 times in total.
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Re: Add switch to dual drives to allow booting from either/or?

Post by 1024MAK » Sun Apr 28, 2019 8:38 am

The Acorn 8 bit computers use the Shugart floppy disk drive interface (or “Shugart bus”).
This allows for up to four devices / drives to be connected. However, Acorn only provided control signals for two devices / drives.

Note that rather confusingly there is no standard numbering. Some manufacturers count the devices / drives from 1 to 4 while others count from 0 to 3.

Logically the first device / drive is controlled by the signal on pin 10 of the interface connector. This is /DS1 (device / drive select 1). Or in the alternative numbering, /DS0.

The second device / drive is controlled by the signal on pin 12 of the interface connector. This is /DS2 (device / drive select 2). Or in the alternative numbering, /DS1.

To swap around which device / drive responds to which signal is simple. Just wire the appropriate signal to the appropriate device / drive.

Now apart from modern drives intended for use with IBM compatible PCs, drives include jumper shunts / links to select the control line that they will respond to.

So if you want to use a switch to swap around which which device / drive is the first logical unit and which is the second logical unit, you need a double pole double throw switch (DPDT). This then needs wiring up to either the interface cable, connector or to the pin headers on both the devices / drives where the device / drive select jumper shunts / links are.

It is even possible to have more than two, but a maximum of four devices / drives connected up. Only two will be active at any time. But the wiring of the switches gets considerably more complex.

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Re: Add switch to dual drives to allow booting from either/or?

Post by 1024MAK » Sun Apr 28, 2019 9:02 am

So for two devices / drives, wire up like this:
27E9B0B8-EEBD-42D5-B633-FDB608C6A927.jpeg
DPDT switch for floppy drives
You can cut the ribbon cable and then wire the above circuit into the wires for pins 10 and 12.

Note that this assumes that both devices / drives will be wired in parallel and that both have jumper shunts / links for device / drive selection. One should be jumpered to be device / drive 1 (0) and the second should be jumpered to be device / drive 2 (1).

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Re: Add switch to dual drives to allow booting from either/or?

Post by colwilliamsnz » Sun Apr 28, 2019 9:11 am

Perfect, thanks so much for the help here. I have a suitable switch so plan to install this scheme directly into the ribbon cable :) Bad weather tomorrow so might just get it done then!

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Re: Add switch to dual drives to allow booting from either/or?

Post by MartinB » Sun Apr 28, 2019 10:28 am

colwilliamsnz wrote: I have a suitable switch so plan to install this scheme directly into the ribbon cable....

I've sold several refurbed drive packs on ebay over the years with a boot switch.

Here's a typical example of my take on the cable-mounted version of the switch where I usually use large-bore heat shrink to secure the mod.....


DDNov17-5.JPG


If it's a bespoke double-pack in a single case, then I usually internally mount the mod....


drive3.JPG


.
Last edited by MartinB on Sun Apr 28, 2019 10:34 am, edited 1 time in total.

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Re: Add switch to dual drives to allow booting from either/or?

Post by DutchAcorn » Sun Apr 28, 2019 12:43 pm

A cable modification would work, but I’d prefer to put a switch on the DS jumpers on the drives (assuming the 3.5” has those).
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Re: Add switch to dual drives to allow booting from either/or?

Post by AndyF » Sun Apr 28, 2019 2:40 pm

I have to say I prefer the DS mod where it is possible even though it can be a bit of a "£$"£$"£ with some of the modern 3.5"s to do it, over and above the cable swap method.

There was something I read why you should not do the cable method but it is highly possible this was not Acorn related and may of well referred to the AMS 3" (yes I know) drives or something to do with the 'ready' signal which is not really relevant here. :oops:
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Re: Add switch to dual drives to allow booting from either/or?

Post by guesser » Sun Apr 28, 2019 2:47 pm

You may be thinking of the mod that some people do for Spectrum +3 external drives which just grounds out a pin causing the drive select to be overridden instead of properly swapping lines? That shorts the output of a 74HCT04 inside the machine. :shock:
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Re: Add switch to dual drives to allow booting from either/or?

Post by AndyF » Sun Apr 28, 2019 2:51 pm

guesser wrote:
Sun Apr 28, 2019 2:47 pm
You may be thinking of the mod that some people do for Spectrum +3 external drives which just grounds out a pin causing the drive select to be overridden instead of properly swapping lines? That shorts the output of a 74HCT04 inside the machine. :shock:
I cannot recall exactly why. I know with my 'B's I've always done the DS mod (usually cursing at the tiny links once I'd found them) but never really had a problem! :D

In regard to the +3 I do have an internal 3.5 in mine actually but I went out my way to purchase the CPC6128 'adaptor' cable that was floating about at the time to do it, no messing about and it all works, electrically at least. Physical mounting/tidyness is another matter. :oops: The only caveat here is to watch out for the curiously swapped 12/5 volt feeds on the 3" drive! Not a problem as I did not bother with the 12v for the 3.5" :D

Back on topic did W.E not offer some kind of 'switchbox' to do what the original poster requested 'back then' ? Unless I am thinking of something else. I know they made a large range of both weird and wonderful products. :D
Last edited by AndyF on Sun Apr 28, 2019 2:52 pm, edited 3 times in total.
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Re: Add switch to dual drives to allow booting from either/or?

Post by 1024MAK » Sun Apr 28, 2019 3:48 pm

The circuit in the diagram I posted here does not have to be cut into the ribbon cable.
You can use suitable PCB mounting header connectors (that IDC connectors will mate with) and a piece of stripboard and use this to breakout the two drive select lines. The same board can be used to bypass the drive selection links in each of the floppy drives if you wish.

If constructed correctly, it will not cause any damage to either the computer or the devices / drives.

Mark
Last edited by 1024MAK on Sun Apr 28, 2019 3:48 pm, edited 1 time in total.

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Re: Add switch to dual drives to allow booting from either/or?

Post by jgharston » Sun Apr 28, 2019 4:25 pm

It's what I did with my floppy drives here (with an additional switch to allow swapping the 3" drive in):

Image

Code: Select all

$ bbcbasic
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(C) Copyright J.G.Harston 1989,2005-2015
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Re: Add switch to dual drives to allow booting from either/or?

Post by flaxcottage » Sun Apr 28, 2019 5:26 pm

1024MAK wrote:
Sun Apr 28, 2019 3:48 pm
The circuit in the diagram I posted here does not have to be cut into the ribbon cable.
You can use suitable PCB mounting header connectors (that IDC connectors will mate with) and a piece of stripboard and use this to breakout the two drive select lines. The same board can be used to bypass the drive selection links in each of the floppy drives if you wish.

If constructed correctly, it will not cause any damage to either the computer or the devices / drives.

Mark
Yep, that's what I did.
IMAG1572.jpg


I can plug in a couple of single drives to make a dual drive system and switch either to be drive 0.

BITD Watford Electronics produced something they called a 'Data Duck'. This was similar to the picture above except for the switch and being much smaller and neater. If you wanted to swap which drive was drive 0 it had to be done manually. I have one and use it to make a dual 3.5" and 5.25" drive from two singles. There is no need to swap drives as I want the 3.5" drive to be permanently drive 0.
Last edited by flaxcottage on Mon Apr 29, 2019 3:53 pm, edited 1 time in total.
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Re: Add switch to dual drives to allow booting from either/or?

Post by colwilliamsnz » Mon Apr 29, 2019 2:16 am

Thanks for all the input. Very useful. In the end I opted for a cable hack inside the case. Works well and pretty tidy I reckon?
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Re: Add switch to dual drives to allow booting from either/or?

Post by MartinB » Mon Apr 29, 2019 6:38 am

Perfect.... =D>

That's also what I do for a dual-drive/single-case pack and if twinning a pair of single-drive/single case units then I cable-mount the switch.

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Re: Add switch to dual drives to allow booting from either/or?

Post by 1024MAK » Mon Apr 29, 2019 8:40 am

👍 8)

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Re: Add switch to dual drives to allow booting from either/or?

Post by BeebMaster » Mon Apr 29, 2019 12:49 pm

Very nice idea, and here's me for nigh on the last 30 years when I've wanted to boot from a disc in drive 1 actually ejecting the disc, and putting it into drive 0!

What a mistake-a de make-a!
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Re: Add switch to dual drives to allow booting from either/or?

Post by MartinB » Mon Apr 29, 2019 3:58 pm

Come on Ian, pay attention! We first discussed this boot switch on here back in 2009 :shock: so there's simply no excuse... :)

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