General Stuff(tm)

[stephen_usher]

Twelve hours later and the PCBs are still only 37% done.

[stephen_usher]

*grumble* Still not finished.

10:40am: They're at last in packaging, but probably missed today's dispatch.
11:30am: Ready for shipping.

[stephen_usher]

Decided to upgrade another QL to use the Minerva ROM this evening, but because of issues with the 74LS04 hack to allow the use of a standard 27C512 I chose to use a GAL.

The QLs two ROM sockets are identical other than for the CE line (active high), with both ROM sockets having a shared OE (active high). CE on the second socket can therefore be used as a proxy for A15 on the ROM. If you invert OE you can use that for the /OE and /CE lines on the ROM, which is what the '04 hack does.

However, the ROM is supposed to take up only 48K of the 64K address space and seemingly the system's ROM address decode logic doesn't seem to turn the second socket's CE line off above the 32K mark, so the ROM is active when the system is trying to access the external ROM socket.

So, my idea was to turn the /OE & /CE signals off if CE and A14 are active at the same time, which effectively turns off the upper quarter of the EEPROM.

Anyway, this is what it looks like. I decided to add A15 as a separate connection and use the GAL rather than trying to solder two wires to the same pin.

IMG_3785.jpeg

[stephen_usher]

Oh, it seems that the PCBs may make it here today after all. They arrived at Heathrow at 6am and are now apparently out for delivery.

[stephen_usher]

And amazingly they've arrived!

IMG_3786.JPG

[stephen_usher]

The old and new PCBs side by side.

IMG_3788.jpeg

I quickly fitted the connector to the new board to make sure I'd got the power and ground the right way around. I'm always paranoid about this. :-)

[stephen_usher]

The new board has been made up and looks quite nice:

IMG_3798.jpeg

Some "issues" to begin with due to my GAL code being very wrong. With the help of people on the QL discord channel I realised that the original logic using NOR gates (74LS02) had completely confused me and I had a lot of the address decode backwards!

Anyway, it works now. Yay!

I think the next task will be designing a case for it to be 3D printed.

[stephen_usher]

More tests on the new board this morning, and cleaning the Microdrives in preparation for the attempt to duplicate originals onto floppy.

For the first time I've managed to copy a large file from Microdrive to HFE file. Maybe it's the new board or maybe it was because I specified the complete set of information in the form, I don't know.

[stephen_usher]

OK, the project is now up on Github. https://github.com/stephen-usher/OPD-Co ... -Interface

[stephen_usher]

This afternoon I finally got around to trying the set of original ICL OPD Microdrives. I hoped that I could get a complete set of the utilities and all the demonstration programs, including a snake game. It didn't quite work out.

I triple tested the floppy interface and the Microdrive drives first to make sure that I had the best opportunity to save any files and then got down to re-felting the cartridges. All good so far.

I put the Welcome cart into the drive and tried to get a listing... The system couldn't read it. I could hear the tape running correctly but the system just didn't see any valid data and would run the drive for a few seconds before erroring out.

Second cart... Not quite as bad. The Demonstration cart ran for a couple of times through the tape before erroring out.

Third cart... The help files for the Psion Exchange office suite... I got a listing! But every time I tried to copy a file it errored out.

Finally, the last cart, BASIC... Just like the first, couldn't even read any valid data and errored within seconds.

Oh well, at least it will make a nice display item at the exhibition.

The next part of the project is to design a 3D printed case for the floppy interface.