Using Microdrives Today

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Mr_Navigator
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Using Microdrives Today

Post by Mr_Navigator »

I am not sure if this should be in this Forum area or not but I will pose the question.

Has anyone connected up microdrives QL/Spectrum to another computer/electronic interface other than the QL or Spectrum and got them to work? Is there any documentation for them that would assist such a project.

The reason I ask is multifold.

Firstly in the process of a project weening off the QL hardware, such things to go are microdrives in place of 5.25 and 3.5 inch disc drives. However there is still a lot of stuff in lofts/garages that occasionally turn up micro drive tapes and eventually the hardware to put them in will no longer exist. So one project that I have been thinking about starting is replacing the microdrives with SD card slots. But what to do with the micro drive hardware? throw away? well with a bit of ingenuity maybe put them in their own case. But how to connect them up to the QL? I need some circuit diagrams.

Having lurked on eBay I have recently obtained Spectrum microdrives for a bit of inspiration, and suitable cables to inspect and copy and adapt for the project.

But this got me thinking even more, yes I can connect them up to a Spectrum, yes I can connect them up to a QL but what about connecting them up to a PC or other computer device with say a USB port that is running emulation software. With Qemulator on the PC or the MAC saving via a USB connection to an actual micro drive, how cool would that be? but has it been done, can it be done?

I presume some form of electronic interface converting signals from the micro drive connector to a USB or some other port would be needed plus some form of driver. The first part would be knowing the connections to the micro drive and what controls it plus the signals, where can I obtain that?

Dilwyn's site? Well there is the Technical Manual but that is not relevant enough, the service manual looks a possibility but has PIC file files which I now have to convert. So now I am looking for a PC based PIC to other graphic file converter...


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tofro
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Re: Using Microdrives Today

Post by tofro »

Actually, you're right - It's the QL Service manual you want to read in order to understand how Microdrives work. The QL technical Manual is mainly software.
The Microdrive inner workings are somewhat hard to grab - Some of it is in the 8049, some in the main processor, some in the 8302(?).
And I very much doubt you'd be able to get something going with respect to connecting to modern hardware without a major investment in non-standard circuitry.
I could imagine something could be achieved by connecting an AVR µC or Arduino via USB to a PC. The hardware of an Arduino Mega (Even a Nano, which is USB-Stick sized) should have all the facilities needed to drive the Microdrive electronically. What you'd need is re-engineering the Microdrive software logic from the 8049 and QDOS, which I guess would be a nice project, but also kindof a challenge.
Problem is, there's not much documentation around on how these beasts actually work. You'd need to look into the service manual, the 8049 sources and a good QDOS disassembly in order to get into grips with Microdrives (and I guess, that it is, counted by the effort to be invested, not worth doing, apart from the academic challenge. And I also guess, that by the time the you had something going, the last MD casettes would have died from age....)


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nichtsnutz
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Re: Using Microdrives Today

Post by nichtsnutz »

Hello all,

the "QL advanced users guide" book has also informations on the
microdrive format in one appendix.It is very informative.

The microtapes are really a pain when you only have a plain QL.
I have only seven microtapes left functioning beside the four originals
and it really gets frustrating today to work with them.I would say that none
of my microtapes has been working for more than five hours before it
worn out.

So,the point for me would not be to connect the microdrives to another
computer,because there are no new tapes for it.It would only make sense
for transfering the microtapes to the PC.But for this there are other
build in possibilities,I have used the serial port.

But it would be really nice to reverse the inner function of the ZX8302 ULA
that is driving the microdrives.The 8749 has no function for the microdrives,as
far as I know.
I had started to try to understand the function of them with the help of
a JM disassembly I found on dilwyns site.I have also connected a spare ZX8302
ULA I have to a XC95108 cpld device to be able to drive the register
individually an see what is happening.Basically the signals are comming
out of the ULA on the RAW1/RAW2 pins and are FM modulated,with a bitcell
of nominal 10us.If a bitcell has an edge in the middle then it is a '1' else
it is a '0'.Now the QL writes GAPs on the tape to be able to detect the
beginning of the sector header and the sectors themselves and the ZX8302 ULA
has a decoder hardware inside that is able to detect these GAPs.I was not
able to understand how exactly this works.There is a bit in one of the ULA
registers that shows that a GAP has been detected and it also fires an IRQ.
Decoding of the FM data is also done in the ULA and the bytes of every RAW
track can be read out of the register.When writing data there is only one
register in the ULA that is alternated between the RAW1/RAW2 tracks.
I had took some logic analyser shots of the ULA signals,but to find out the
correct timing and working of the hardware will be a very time consuming
thing.

The last aim would be to use a modern cpld+pic controller to code/decode all
the data and store them on SDCard.The advantage would be that no software or
driver would be needed.
You could just use again the plain QL and type "dir mdv1_" without the
fear that it could be the last time...

Greetings,
Vasilis

The image shows a recorded sector header,left and right from it are parts of the GAPs as they are
detailed in the "QL advanced user guide".I had also decoded the sector header data by hand!
sh.png
I think this would be a project for the whole next year...


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Mr_Navigator
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Re: Using Microdrives Today

Post by Mr_Navigator »

Wow thanks guys for the comprehensive response, I will need to do a bit more reading methinks. Actually on a second look I probably need to do alot more reading.

It does beg the question what to do with a knackered microdrive tape that no longer works with the QL (which is why I first started thinking about the possibility of the non-QL connection), as on the outside they would look absolutely fine (except for the biro/pencil scribbles)

If an alternative method is not viable for their continued use as a storage device then perhaps as part of an valuable artifact/trophy hmmmnn


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polka
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Re: Using Microdrives Today

Post by polka »

What I noticed : often the tapes will not read because the very little pressor pad is worn out and the tape is not continuously touching the magn. head.

You may by "microsurgery" replace the original pad with "felt" cut off the "lips" of 135 film cartriges (if you still do analog photography :mrgreen: ) ; this way, I always successfully restored reading on a few cartriges that I needed to access, but I did not do it systemeatcally on all - now I will not even try to read another one unless I first performed this "upgrade" on it.

Paul


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tofro
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Re: Using Microdrives Today

Post by tofro »

Side Note on the QL Service Manual:

If you think it's a major hazzle to convert the PIC files of the QL service manual into something you can actually read on modern hardware, check

ftp://ftp.worldofspectrum.org/pub/sincl ... Manual.pdf

for a .pdf version.

Cheers
tofro


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M68008
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Re: Using Microdrives Today

Post by M68008 »

This would be a cool project! I have many MDVs that beg to be read. Although not sure if they may still be readable at all.
Microdrives are high speed magnetic tapes, so my guess is that another solution might be to just use the interface to power the motor and redirect the output signals from the tape head to another circuit, maybe demodulate them and send them to an A/D converter. Any further decoding would then be a software problem on the PC. Perhaps the bitrate is low enough that a high end audio interface on the PC could be used for the A/D conversion? As a Microdrive contains about 100 KB of data plus extra bits (gaps, headers) and the entire tape runs under the head in 7 seconds, I think this would place the bitrate per track at about 75-80 kbps.


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vanpeebles
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Re: Using Microdrives Today

Post by vanpeebles »

It would be a great project and superb(if not vital) for making archive dumps of microdrive programs before they are lost for good. I often complain about the QL scene not being as serious as the speccy one when it comes to software preservation. They have perfect dumps of tapes and all kinds.


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Mr_Navigator
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Re: Using Microdrives Today

Post by Mr_Navigator »

It would be a great project and superb(if not vital) for making archive dumps of microdrive programs before they are lost for good. I often complain about the QL scene not being as serious as the speccy one when it comes to software preservation. They have perfect dumps of tapes and all kinds.
I believe RWAP already does this.

I think the RWAP Master said somewhere on this forum with Tookit II I believe, something like (dont quote me) 'FORMAT RAM1_, MDV1_' RWAP will correct with the appropriate syntax

This would put into memory errors and all, the whole contents of MDV1_


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Re: Using Microdrives Today

Post by RWAP »

The correct format is:

Code: Select all

FORMAT ram1_mdv1
This makes a direct image to ram disk of the microdrive, with any corrupt files suffixed by a *

Daniele Terdina has also written a short program to make an image of a microdrive and store it directly on disk - it is not as good as recovering corrupt microdrives as the above example, and does not currently like non-standard QLs (ie Gold Card / Super Gold Card).


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