The Sinclair QL Forum

Hi Martyn,

Here are some screen dumps from the oscilloscope.

Sector timings and gaps. Gap between header and data record. Data start. Track 1 is yellow. Data end. Track 1 is yellow. Data timing Thanks allot!

Antony

Hi Anthony

On first inspection, the only things to stand-out are the over/undershot/ringing of the RAW signal lines and also the very sharp falling edges.

The ringing may just be an artefact of the scope probes, but given the age of the QL ULA, I wouldn't be surprised if those voltage 'excursions' are upsetting the ULA electronics..

From speaking with Charles Ingley some time ago, we suspect that the ULA is of a hybrid digital/analogue design and between it and the MDV ULA itself (on a real unit), just use voltage shaping to create a digital-like signal.

The cleanliness of your falling edges might, counter-intuitively, indicate an incorrect drive circuit as (again, somewhat speculatively, and after chatting with Dave Park about it last year) we suspect the use of an 'Emitter-follower' type output (I think I've used the right term), which typically gives sharp rising edges, but lazy falling edges, with a definite slope-off - which the ULA copes well with.

You can observe these lazy falling edges in traces of real MDV units which are read well enough by the ULA.

[EDIT: I have attached a one-page document that includes some sample MDV traces from a real unit clearly showing the typical slope of the falling-edge - that was written-up to replace the rather blurred page present in the QL Technical Service Manual (Appendix D5). Compare figures D3, D5 & D8.]

You'll notice that both the QL and the Spectrum/Int-1 include passive pull-down resistors on each RAW line (across 10k ohm to 0v in the Int-1 and 33k ohm to -12v on the QL.)

If the ringing is the problem, placing a capacitor across each RAW line (figure out a reasonable RC constant) might help - the line amplifiers in the ULA will re-shape it.

Just some initial thoughts, anyway...

Keep us posted!

Eventualy I found the problem. It was with the checksum of the file info block. It seems it is wrong in most of the MDV you can find on the net. After fixing the checksums it worked!

kladogen wrote: ↑Mon Aug 14, 2023 10:07 pm Eventualy I found the problem. It was with the checksum of the file info block. It seems it is wrong in most of the MDV you can find on the net. After fixing the checksums it worked!

Very interesting....

kladogen wrote: ↑Mon Aug 14, 2023 10:07 pm Eventualy I found the problem. It was with the checksum of the file info block. It seems it is wrong in most of the MDV you can find on the net. After fixing the checksums it worked!

If you are referring to Qemulator Mdump2 .mdv image files. The checksum on the data blocks are the wrong way round for a QL.

Normally on the QL the checksums are in little endian format, but the Qemulator checksums are stored in big endian format. So if the checksum is supposed to be $12AB, it is stored in a real microdrive cartridge as $AB12

If it's MDI image files your having problems with. The MDI driver is supposed to maintain the checksums. But I never actually uses them. So there could be problems there.

I don't know if the checksums in QLAY image files are maintained correctly. But I don't think I have encountered any problems during my testing of them.

Upload an image file you are having problems with and I will have a look at it.

OqtaDrive 0.5.2 has been released. It's mostly a maintenance release, but there's also one new feature: support for Qemulator mdump (V1 & V2) formatted MDV files, as well as MDI files.

xelalex wrote: ↑Tue Sep 19, 2023 8:55 pm OqtaDrive 0.5.2 has been released. It's mostly a maintenance release, but there's also one new feature: support for Qemulator mdump (V1 & V2) formatted MDV files, as well as MDI files.

Excellent, I have an internal Oqtadrive to make.

Well I have external PCBs to make as well.

Hi,

A question concerning the Oqtadrive, which uses a Raspberry Pi, for WIFI connection and storage.

Can the Oqtadrive be used without a Raspberry Pi, using the Arduino SD Card slot to store the microdrive images?

Derek_Stewart wrote: ↑Wed Nov 08, 2023 6:03 pm Can the Oqtadrive be used without a Raspberry Pi, using the Arduino SD Card slot to store the microdrive images?

No, that's not possible. The Arduino is really just a protocol converter. It needs the daemon process to run somewhere, for example on a RaspberryPI, which then does the majority of the work.

Hi,

Thank you for the clarification.

Pity microdrive images could be transferred to the Oqtadrivd storage by direct connection, for people without WIFI

Maybe thd QL needs a WIFI solution

I have PCBs for the internal and extetnal Oqtadrive, I have also some 3D Printed cases for the external Oqtadrive.

Now I have not much to do I will look at getting the Oqtadrive built.