OPD: Computer One RAM Expansion

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KINGCHEF
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OPD: Computer One RAM Expansion

Post by KINGCHEF »

I also have a gadget that adds re-writable memory space in a capsule slot. I, at first, thought it might fit the bill as extra memory but I don't know enough about the way the OPD logs in the Capsules to the map. Anyway it was a late development from ICL . It has 4 x surface mounted memory chips, one other IC, a backup 3v battery and a switch. The PCB doesn't look TOO difficult to copy, says he never having done one :-). The idea being to load a lump of code into the capsule then flip the switch to retain the contents of the memory so the OPD could be restarted and the progarm or w.h.y. then logged into the program list. Might be somewhere to put the extra memory code? Pictures available.
OR could the code be burned onto a ROM and set in a capsule. I've done several conversions of capsules, removing the ROM and substituting a socket.
As I remember, the OPD needs to start up and log inthe memory code then do a reset to get it to work.

David


KINGCHEF
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Re: OPD: Computer One floppy interface recreation.

Post by KINGCHEF »

Hi,
Lost my post somewhere

Murray McCabe did some work on memory upgrade for the OPD. He used the memory code from the Teledrive to log-in the space into the map?
I have a, currently not working, mainboard where I did the upgrade, replacing the memory chips with 256s on sockets. I don't remember why I stopped using it but I think there was conflict with the Teledrive so I couldn't use it with the disc drives. I don't think it was tested with the C1 i/face. I think I have the code dump from the ROM in the Teledrive but it might be added to other programs to be used with the daughter board ROM upgrade. I can look it out if anyone is interested.

David Warne


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Re: OPD: Computer One floppy interface recreation.

Post by stephen_usher »

KINGCHEF wrote: Tue Jul 09, 2024 12:19 pm I also have a gadget that adds re-writable memory space in a capsule slot. I, at first, thought it might fit the bill as extra memory but I don't know enough about the way the OPD logs in the Capsules to the map. Anyway it was a late development from ICL . It has 4 x surface mounted memory chips, one other IC, a backup 3v battery and a switch. The PCB doesn't look TOO difficult to copy, says he never having done one :-). The idea being to load a lump of code into the capsule then flip the switch to retain the contents of the memory so the OPD could be restarted and the progarm or w.h.y. then logged into the program list. Might be somewhere to put the extra memory code? Pictures available.
That would be a writable ROM basically, so you could write a ROM image to it and then reset the machine. It's not the same as extending the RAM.

The Teledrive basically patches the system ROM so that when it detects and invalid ROM the Teledrive code then checks to see if there's RAM there and then patches the memory map in RAM to add it to the pool of 4K pages the system can use.

Replacing the RAM in the system won't work properly due to the brain damaged memory map design in the OPD with I/O interspersed with the ROM slot locations. It was designed not to be upgraded and obviously the designer thought that 128K was mega huge and no-one would need more, as all programs would be running from ROM and the RAM would just be workspace.


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Pr0f
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Re: OPD: Computer One floppy interface recreation.

Post by Pr0f »

KINGCHEF wrote: Tue Jul 09, 2024 12:28 pm Hi,
Lost my post somewhere

Murray McCabe did some work on memory upgrade for the OPD. He used the memory code from the Teledrive to log-in the space into the map?
I have a, currently not working, mainboard where I did the upgrade, replacing the memory chips with 256s on sockets. I don't remember why I stopped using it but I think there was conflict with the Teledrive so I couldn't use it with the disc drives. I don't think it was tested with the C1 i/face. I think I have the code dump from the ROM in the Teledrive but it might be added to other programs to be used with the daughter board ROM upgrade. I can look it out if anyone is interested.

David Warne
That would be appreciated David :-)


KINGCHEF
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Re: OPD: Computer One floppy interface recreation.

Post by KINGCHEF »

Hi,
Flash of memory...... Murray actually used the code from the early Memory Expansion Unit not the Teledrive.

I have a ROM dump of a 512 ROM with Basic and the memory code combined. Basic is too big for a 256 so spills over into a second.
I have isolated what I'm sure is the Memory Code and saved it as a separate file. I intend to send both. So how do I send you a 64k file and a 28k file?

Also I suppose it would be possible to split the 512 into 2 x 256s and put them on a pair of capsules. Not sure. I have ROM dumps of 2 x 256s that purport to be Basic pt1 and Basic pt2 for just that implementation but the files look identical so a glitch has crept in somehow.

David


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Pr0f
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Re: OPD: Computer One floppy interface recreation.

Post by Pr0f »

I think that 512 image would be ideal - as I need to put basic into a ROM, and the rest of it is otherwise waisted space... Basic is about 36K, so just over that magic 32K barrier :-(

You should be able to attach the image in a zip file I think.


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Pr0f
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Re: OPD: Computer One floppy interface recreation.

Post by Pr0f »

Could one of the mods seperate out the RAM expansion into a new thread - pretty please :-), that way we can keep the disk interface thread clean :-)


KINGCHEF
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Re: OPD: Computer One floppy interface recreation.

Post by KINGCHEF »

Hi

Will send file.

The Memcode starts at 9314 with ~SMEUPATCH

System didn't like .BIN or .HEX files so in a zip as suggested. Zipped up .BIN file

David
Attachments
OPDBasicAndMemoryCodeForExpansion512.zip
(32.09 KiB) Downloaded 9 times


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Re: OPD: Computer One floppy interface recreation.

Post by stephen_usher »

Very interesting.

May be useful for at the very least a 16K or 24K SRAM module (using simple address decoding) or even 32K with simple paging out of the ROM.

(e.g. at initialisation the ROM copies code into the SRAM and then jumps to it. This code toggles a flip-flop which deselects the ROM and selects the SRAM for low addresses and then sets up the OS memory pages to use the RAM. The base address can be obtained by the code reading the program counter. It may have to use the bottom 4K for a stub routine and ROM header in case the OS tries to call it).


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Re: OPD: Computer One floppy interface recreation.

Post by vanpeebles »

Pr0f wrote: Wed Jul 10, 2024 6:31 pm Could one of the mods seperate out the RAM expansion into a new thread - pretty please :-), that way we can keep the disk interface thread clean :-)
Done :)


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