Recreate OSI machine

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Steve Gray
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Joined: Mon Oct 06, 2008 1:54 pm
Location: Markham, Ontario, Canada
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Recreate OSI machine

Post by Steve Gray »

Hi All,

Not too much activity lately, so I thought I'd post about something I've had in the back of my mind for a while.

Has anyone thought about recreating an OSI machine from "newer" parts? Not new like FPGA, but new as in individual components. You could replace all the original 2114 ram chips with one 32Kx8 static ram chip, all the OS ROMS with one 32K EPROM etc and drastically reduce the chip count to make a new machine. It's kinda like the Replica Apple I, or MicroKim.

Actually, I know someone recreated the UK-101 this way, but it had no video out. I think the video circuits would be the hardest to simplify/recreate unless you used a CRT controller chip like the 6545/6845, but then you'd have to patch the roms to initialize the chip. Not a big deal.

Any thoughts?

Steve
C4P working, C1P working. 600D Replica working, C4P+D&N floppy not working. 505 board, 610 board, Mittendorf board, TOSIE hacker board need testing, PicoDOS disk untested.
dave
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Posts: 710
Joined: Tue Sep 09, 2008 5:24 am

Re: Recreate OSI machine

Post by dave »

The OSI machines should definitely be easy to replicate. Like you said, you could definitely cut down the parts where multiple identical parts were used because of small scale (memory). The video is mostly a bunch of counters and some logic, and a shift register. If you're not against using an FPGA for the non-CPU portion, you could probably squeeze all the video including RAM/CGROM, and a disk interface (6851/6821) on an FPGA. If you don't want an FPGA, but don't mind programming a PIC, you could also probably use a single microcontroller (with enough pins) to emulate the video circuitry (including CG ROM), and serial / floppy interface. Or, you could just bite the bullet and recreate the video with the best small-scale logic available today. A 6845 would be something of a departure, but probably not too hard to program if you're not afraid of modifying the monitor ROM. However, if you do that, you may as well just leave out the video and use a serial terminal.

I'd love to know if you ever actually do this. I'd also be interested in the progress of the FPGA OSI implemtations out there.

Best regards,

Dave
Steve Gray
Posts: 321
Joined: Mon Oct 06, 2008 1:54 pm
Location: Markham, Ontario, Canada
Contact:

Re: Recreate OSI machine

Post by Steve Gray »

Giving a second thought to the video, I'm not sure a 6545 controller chip would be able to switch between 64 and 32 columns with a single line from the latch at $DE00. Any recommendations for a PIC? I did a web search and all the PIC-based video solutions seemed to only handle very low resolution... nowhere near being able to do 64 columns. I'm sure an FPGA solution would be feasable as I've seen fpga implementations of some pretty complicated video chips (ie: Amiga). Unfortunately I have no experience with this kind of stuff, however being a programmer I guess it wouldn't be that hard to pick up.

Steve
C4P working, C1P working. 600D Replica working, C4P+D&N floppy not working. 505 board, 610 board, Mittendorf board, TOSIE hacker board need testing, PicoDOS disk untested.
dave
Site Admin
Posts: 710
Joined: Tue Sep 09, 2008 5:24 am

Re: Recreate OSI machine

Post by dave »

I think a PIC could do it, especially if you use one with lots of I/O lines and a 40 MHz clock (or even a 20 MHz clock). The 540 boards used a 12 MHz dot rate. If you use an 8-bit shift register at the output, you can probably make the timing. I wonder if it would be possible to hijack the UART for that purpose and save 7 I/O lines. You can use internal RAM for the video mem, and 18 I/O lines for address and data. I bet that ultimately, a small FPGA would really be much easier, though, especially if you want color. Personally, I'd just as well fix up and old machine. . .
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