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Eurorack modular 8085 computer
ChristofferB:
Hey! I'm currently setting out to build the 8085 system, and thought I'd share.
The computer is going to be modular, with each card being as universal as possible.
I'm sticking strictly to the 19'' 3U subrack Euro Card Bus standard, A) because it's not very widely seen in DIY computers and B) because it's just a convenient form factor, I think.
Mechanically that means:
- 3U subrack with DIN 4.1612 AC connectors to backplane
- PCB sliding rails
- Either proper eurorack front panels with handles (a bit pricey) or pcb's without handles
- 16cm x 10 cm std. vero-boards for creating the circuits on (probably with vero-wire)
Computer wise, I plan on distributing the boards as such:
- CPU card: 8085, clk, bus drivers, reset
- RAM/ROM card(s): Plan on going for 8k*8 RAM/ROM - will have decoding and type patchable for universality.
- Serial card: (8250/8251), baudrate gen, etc
- Display/keypad card: Hex keypad and 7seg displays, either with an 8279 or some 8255's
Display and keypad won't be on the module plate. I think I'll add a separate 3U front plate above for that. (and other controls, too) - Just neater that way.
- Cassette interface card (for when I get a 19''rack reel to reel for it)
- 8255 parallel centronics printer interface
Aand in the further future:
- CRT card (I have not looked into driving a CRT
- ASCII keyboard card (not difficult, but not that useful without a CRT as display)
- Punched tape interface (Yeah, like I ever find a rack paper tape reader)
- 8088 CPU card (maybe)
I'll try and stick to 74LS and HCT logic (I have so much LS, but HCT would be easier on the PSU)
And 82XX intel peripheral IC's.
I'm aiming for using the standard ECB pinout for the bus, but I have to make some modifications. The standard has specified z80 interrupt lines, but no /INTA for intel CPU's.
Lastly, I need some bus termination, I think. I plan on just adding that to the bus side of the CPU card, as you'd usually always have that installed. I think passive resistive termination is enough for now.
Currently working on the power supply, which will be 5V, at first. Later, a +5 +-12V will probably be needed.
I'm not sure if I should have more features on my CPU card than I've planned. Right now, it's literally only the CPU module.
Let me know what you think! Has anyone ever worked with the 3U subrack /ECB standard?
Is there any cards / functionalities you'd add?
--Christoffer
MK14:
Surely with specs like that (8085 etc), you may want to try/use CP/M. Hence want at least a (8085 era) floppy, to more easily allow that.
I never make jokes, on forums. With your 8088 cpu, and paper tape unit, by creating 8088 compatibility versions, of some of the newer (needed) instructions. You can download/transfer win10, onto 1,472,446,284 miles of paper tape. Then after about 345,347,399,585 hours, to read the paper tape, you can play with win10.
ChristofferB:
It would at one point be nice to be able to run some "real" software, and not just small homemade routines.
5 1/4 inch floppy drive (dual?) would be convenient, if not necessary for that. I'll add that to the list!
Running win10 from paper tape would be "a bit" ...ambitious... but If I do upgrade to 8088, it'd be nice to be able to run IBM DOS.
--Christoffer
MK14:
--- Quote from: ChristofferB on March 21, 2016, 01:56:17 am ---It would at one point be nice to be able to run some "real" software, and not just small homemade routines.
5 1/4 inch floppy drive (dual?) would be convenient, if not necessary for that. I'll add that to the list!
Running win10 from paper tape would be "a bit" ...ambitious... but If I do upgrade to 8088, it'd be nice to be able to run IBM DOS.
--Christoffer
--- End quote ---
I think you would find, trying to run IBM DOS (or similar), a MASSIVE undertaking. Because (presumably), you would have to turn the 8088 system, into a COMPLETE (compatible) IBM PC, of that era.
E.g. CGA graphics (or whatever standard applies with it), BIOS (compatible with both IT, AND your system), all sorts of other bits and pieces, adding to the major headache.
BUT it may be possible to get hold of a FULLY open sourced "DOS", by the time you are ready. Which lets you configure/compile/tweek it to your particular hardware.
MK14:
--- Quote from: MK14 on March 21, 2016, 02:03:18 am ---
--- Quote from: ChristofferB on March 21, 2016, 01:56:17 am ---It would at one point be nice to be able to run some "real" software, and not just small homemade routines.
5 1/4 inch floppy drive (dual?) would be convenient, if not necessary for that. I'll add that to the list!
Running win10 from paper tape would be "a bit" ...ambitious... but If I do upgrade to 8088, it'd be nice to be able to run IBM DOS.
--Christoffer
--- End quote ---
--- End quote ---
I think you would find, trying to run IBM DOS (or similar), a MASSIVE undertaking. Because (presumably), you would have to turn the 8088 system, into a COMPLETE (compatible) IBM PC, of that era.
E.g. CGA graphics (or whatever standard applies with it), BIOS (compatible with both IT, AND your system), all sorts of other bits and pieces, adding to the major headache.
E.g. Good luck with building your "Compatible Chip Set", out of 1,000? raw TTL 74LS/HCT devices.
BUT it may be possible to get hold of a FULLY open sourced "DOS", by the time you are ready. Which lets you configure/compile/tweek it to your particular hardware.
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