ICL OPD

[stephen_usher]

But the "shutdown" pin doesn't go anywhere other than to one transistor which controls the SRAM. I can't find it going anywhere else. You'd have thought it would have kept the machine from powering up at all until it was high, but it doesn't.

[Pr0f]

On my bare board - the powerdown pin hit's the gates of three of those FETS - the small square items labelled FT1 - FT6, If you have the scanned schematics - there is a readable circuit diagram for the power delivery section - 'page 143' - the FET's are FT1 (controls the relay on the main board), FT5 (2K RAM CE) and FT6 (in the main power regulator circuit) and that also drives FT3 (not sure of it's function)

[stephen_usher]

Oh, OK.I wonder why my system runs without that signal being high. Everything runs except the SRAM. Bad MOSFET maybe?

[Pr0f]

This entry on RWAP site: https://rwapsoftware.co.uk/oneperdesk/t ... _info.html

5. ICL MODIFICATIONS

The following modifications have been seen on the mainboard.

5.1 C10 changed from a 220n, 40v tantalum to a 220n film capacitor in series with a 1ohm resistor
5.2 R47 changed from a 1Kohm resistor to a 2n2 ceramic capacitor
5.3 Field effect transistors FT3 & FT6 are removed
5.4 R11 changed from 33ohms to 200ohms
5.5 A 1Mohm resistor fitted in parallel with the 15MHz crystal

so it seems they took out 2 of the FET's as a modification at some point - I wonder if the standby mode didn't work as they intended?

My board still has all 6 FET's in place.

[stephen_usher]

Mine only has three MOSFETs.

[stephen_usher]

David Warne and Rich Mellor got the Computer One floppy interface ROM image to me today...

Wrote it to EEPROM, set things up, switched on and...

The interface only goes and works first time!

[Chr$]

No way, that's incredible! Hat's off. I assume from Basic you access the floppy with flp1_, just like on a QL? And can the resultant disks (or disk images) be read with a QL/QL emulator?

Will you be making the PCB design and other details public? I'd love to add FDD to my OPD.

[stephen_usher]

I've no idea how to access it from BASIC at the moment as I don't have a fully working version of BASIC as that comes on Microdrive and isn't built in.

As for the design being published. I'll work on a Mk.II which will fix a few things such as the connector having to be on the "wrong" side of the PCB and integrate my clock fix so as to use an crystal oscillator rather than a crystal and capacitors, which didn't work. I can also rework it to be two boards connected via IDC cable so it's not so tall.

[Chr$]

I've no idea how to access it from BASIC at the moment as I don't have a fully working version of BASIC as that comes on Microdrive and isn't built in.

As for the design being published. I'll work on a Mk.II which will fix a few things such as the connector having to be on the "wrong" side of the PCB and integrate my clock fix so as to use an crystal oscillator rather than a crystal and capacitors, which didn't work. I can also rework it to be two boards connected via IDC cable so it's not so tall.

I have BASIC on cartridge and was able to make back-ups of the original in the past. I'd be happy to send you copies. Or perhaps there is a way I can put it on to an OPD floppy image and just send as a file - but then I wouldn't know how to start it as no doubt the menu to enter basic is going to be coded to start it from mdv.

[stephen_usher]

The interface maps the floppies to the left and right Microdrives. As far as the system and applications are concerned it still has only the two Microdrives and nothing else.