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Eurorack modular 8085 computer

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--- Quote from: ChristofferB on April 09, 2016, 09:17:07 pm ---Yeah, that's right, but programmable logic kinda goes that step too far in taking all the fun out of it.

I plan on using a programmable interrupt controller for function keys. That must be the easiest solution. So a minimal bootloader would be:
 - Initialize 8279 (couple of bytes)
 - Initialize interrupt controller (8259 I think) (couple of bytes)
 - on interrupt from keypad, save data to addr, increment addr, repeat
 - run from addr when "run" interrupt key is depressed

I think that could be accomplished in less than 32 bytes.
So two 2x 4-16 decoders and a diode matrix memory could run this without an actual ROM chip.

That would be almost a cool enough waste of time to try!

--- End quote ---

Sorry, I was NOT clear enough in my original post. I meant "*IF*" you were doing it in the modern style. Of course, since you are NOT doing it that way, this section of this thread, is working out ways of doing it. I.e. FPGAs/CPLDs/modern MCUs are rules OUT! (Sorry for any confusion).

Yes I agree, diode ROMS, are real fun. A long time ago, that is one of the methods, they use to use, to do stuff like that. Also because masks are VERY expensive (so only suitable for high volumes or clients with very deep pockets) and originally EPROMS and PROMS did not exist. Diode matrix/steering ROMS, was the way they had to do it. But there were other solutions, I guess.

Another solution. Which would be authentic (time wise, I think). Would be to use a matrix plug board, of the type they use to use in higher end, analogue synthesizers. Hence you would only need to create the boot loader, ONCE, via the plug board. But could experimentally/playfully mess with it, to your hearts content.

But don't worry. Being realistic, I'm sure you are much better off, using the steps, you have recently posted about, to solve the problem. I am really just making conversation here.

If it had been a computer made out of RAW transistors (i.e. 1950s, and NO integrated circuits, whatsoever!), ONLY. Then maybe the plug board would have made more sense.


--- Quote from: MK14 on April 09, 2016, 08:43:00 pm ---...
The next $64,000,000 question is going to be, how small/tiny can you get the boot loader program to be, in order to just load in (or allow to be typed in), a "proper", BIG boot loader program ?

--- End quote ---
Ahhh. I remember back in my days with DEC, working on PDP-11s, we used the front panel toggle switches to thump in about 20 words - then reset the address, and release the RUN switch - to boot the disk controller, and everything from there on was rosy!
Slightly later machines had an Intel 4004 based 'front panel emulator' that loaded the boot code with just a couple of switch actions... but no blinkenlights!

To @ChristofferB

We were talking about your Proms (Intel), and a programmer for them.

The following vintage magazine, seems to include a programmer project for them. I'm not 100% sure if it applies to the ones you have, and/or includes enough details to use. But probably interesting, anyway. It goes into a HUGE amount of detail, into these "new" at the time, Proms. (Maybe you have Eproms rather than Proms, and I don't know if that is similar enough ?).

Example post, where we were talking about it:

--- Quote from: ChristofferB on March 24, 2016, 12:52:41 pm ---Well most EPROM's you find in gear has these metalized, it looks, labels.
I have never had any trouble with accidental erasure, but I'm a bit cautious about photographing a board with flash that has unprotected EPROM's. Might be nonsense, dunno.

I've by the way recently aquired nearly 200 intel 1702 EPROMS (the first commercial eprom, if I recall correctly), but they're 256 bytes and impossible to program, requiring 0V, +5V, -9V,+47V and +56V for programming.

--- End quote ---

Great! that might be useful!
Well they say prom's but they clearly have windows - thus must be EPROMS. Think it's similar enough. I'll keep that in the documentation archive!

Using a smaller microcomputer system to bootstrap could be interesting- maybe an intel 8051?

-The plug matrix is a cool idea, I actually thought about making one such using 3,5mm mono jacks, with diodes in the jack plugs connecting rows and columns.

Diode rom matrix boards are difficult to make on strip/hole/veroboard. The layout is awkward.
Back in the days, there were dedicated cards, with traces lain out for diodes to be fitted easily.


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