External QL microdrive?

[issue5]

Hi there, due to the number of QLs with dodgy microdrives I was wondering if anyone could tell me how the leads from a spare good QL microdrive unit could be connected to the microdrive expansion connections on the right hand side of the QL board - ie. which wire on the microdrive tail goes to which track on the PCB? I do have some spare microdrive connector cables and was considering soldering the stripped cables at one end onto a spare QL microdrive unit, any help much appreciated - other wise I will just be forced to experiment.
Thanks

[Maskenlos]

Hi,

If I understand you correct you want to connect an internal Microdrive to the Microdrive expansion port, right?
This is not possible as some signals are missing. Only external drives, like Spectrum Microdrives, can be connected.

Best regards,

Stephan

[issue5]

Thanks for that Stephan, saves me a lot of messing about for nothing
Cheers
Keith

[klausfrank]

Hi,
I have used the cable between the IF 1, for the Spectrum, and a microdrive unit, and it works.

[Maskenlos]

No doubt, external microdrives work at the expansion port.
But connecting an internal microdrive to that port is not possible

[roninfourseven]

If I am correct, the internal microdrives have specific IDs that can't easily be changed, kind of like SCSI ID. I tried swapping the internal microdrives (my mdv1_ is flaky), which seem to be labelled 1 & 2 and they don't work swapped.

I now have a vMap to use with my vDrive QL, which allows remapping of the IDs. I now have mdv1_ mapped as mdv3_, mdv2_ remains as normal and the external vDrive QL is mapped as mdv1_ so I can boot from mdv images on SD card.

Perhaps a vMap would be the thing for you?

https://vdrivezx.com/vmap/

[tofro]

If I am correct, the internal microdrives have specific IDs that can't easily be changed, kind of like SCSI ID. I tried swapping the internal microdrives (my mdv1_ is flaky), which seem to be labelled 1 & 2 and they don't work swapped.

Nope. The drives don't have IDs - they are addressed by the position in the chain (the mdvs are daisy-chained in their order of connection) - The QL simply addresses the drive by shifting a bit through the chain of drives as a shift register - the one that "gets" the bit is the addressed one. The drives themselves should also work when swapped. (If you "break" the chain, however, by for example removing mdv1, mdv2 will no longer work).

[roninfourseven]

If I am correct, the internal microdrives have specific IDs that can't easily be changed, kind of like SCSI ID. I tried swapping the internal microdrives (my mdv1_ is flaky), which seem to be labelled 1 & 2 and they don't work swapped.

Nope. The drives don't have IDs - they are addressed by the position in the chain (the mdvs are daisy-chained in their order of connection) - The QL simply addresses the drive by shifting a bit through the chain of drives as a shift register - the one that "gets" the bit is the addressed one. The drives themselves should also work when swapped. (If you "break" the chain, however, by for example removing mdv1, mdv2 will no longer work).

Hmm, ok interesting.

I can say for sure that the microdrives in my QL definitely do not work in any position though, as my mdv1 has been playing up and I thought I'd just switch then out, mdv1 becomes mdv2 and vice versa.

It didn't work at all, with neither drive being recognised until I put them back in their original positions. The drives are marked 1 & 2 as per the picture:

I don't doubt you're right, however my own recent experience was that the 1 & 2 units in the QL could not be swapped. Incidentally, this was before I installed the vMap, so it was stock.

[martyn_hill]

Hi Keith!

As mentioned below, without some additional circuitry, the bare QL MDV units can't be connected to the MDV Expansion bus.

That said, it is not rocket science to re-construct the fairly simple circuitry needed and, with the right connectors, the bare QL units can be used via the expansion connector.

The additional circuitry needed is effectively to reproduce the bottom-board of what you find in the ZX MDV units, or built-in to the QL (and OPD) mainboards.

I have done this as part of an MDV 'break-out' board I built to allow me to attach and test a variety of external MDV units - including bare OPD, bare QL and 'full' ZX Microdrive units.

It's probably more effort than you were planning and instead picking up a full ZX Microdrive unit is not too difficult from eBay or SellMyRetro from time to time. The bare units are fiddly to work with, as well.

If you do decide to try attaching a bare drive to the expansion connector, let me know and I'll happily share the details of my break-out board. It can also be used with a ZX Interface-1.

As for the switching round of MDV#1 and #2 - its usually due to a faulty ULA on one of the units which may or may not render that unit dead, but also anything further down the serial 'chain'. Thus you might well find as you did that one works only on the left, but when connected to the right of (faulty) unit, it is also knocked-out of action.

There are other reasons for your observation, however, including the relative susceptability of the given MDV unit to the RF interference generated especially around the PAL video-converter IC that is closer to the left-hand MDV slot. You'll probably notice that the left-hand unit had a make-shift RF-shield around its ULA, whereas the right-hand unit typically does not.

[roninfourseven]

As for the switching round of MDV#1 and #2 - its usually due to a faulty ULA on one of the units which may or may not render that unit dead, but also anything further down the serial 'chain'. Thus you might well find as you did that one works only on the left, but when connected to the right of (faulty) unit, it is also knocked-out of action.

There are other reasons for your observation, however, including the relative susceptability of the given MDV unit to the RF interference generated especially around the PAL video-converter IC that is closer to the left-hand MDV slot. You'll probably notice that the left-hand unit had a make-shift RF-shield around its ULA, whereas the right-hand unit typically does not.

Hey Martyn.

Totally get the serial chain analogy, however my no2 unit does work fine, so I suspect that the no1 ULA hasn't failed, at least perhaps not completely. The no1 unit does respond to commands ok, but doesn't read anything, so it could possibly be a problem with the head I guess, or the drive motor/capstan isn't making good contact so the tape speed is varying. Carts that work fine on the no2 drive, don't work on the no1.

You are indeed correct, my no1 drive does indeed have a small RF shield and the no2 doesn't, so I guess my question is, would the interference prevent the drive from even being detected in slot 1? Or would it merely prevent it from operating correctly, because in y case the QL didn't even see the drive.

I'm interested to understand more as my QL has lain idle for a long time and I now have the space to have it out and use it and am always wanting to know more.

If it was an Atari ST I'd know considerably more, but sadly not!