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Thread: Corona Data Systems PPC-11

  1. #11

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    Quote Originally Posted by rvdbijl View Post
    Mine is a PPC-21, but I'm having keyboard issues, so it's tough to interact with it. Are you looking for a ROM dump? The little 9" screen on mine does have an insane looking resolution. Very sharp. Nicer than the old Compaq portable I used to have.
    I did manage to get the 20MB HDD to spin and lo-and-behold, it actually works and still has data on it. Transferring it now using interlnk/intersvr off a boot floppy. Glad I kept that old parallel port Laplink cable from back in the day!
    Nice!
    Well, if you're willing to dump the contents of the character generator ROM (and have a way to do it), that'd be awesome.

    It's a pity about that nonstandard keyboard connector... although if the protocol and the KB controller are close enough to the standard XT scheme, perhaps it may be feasible to devise a cheap adapter for other XT keyboards?
    int10h.org :: :: :: blog

  2. #12

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    Quote Originally Posted by VileR View Post
    Nice!
    Well, if you're willing to dump the contents of the character generator ROM (and have a way to do it), that'd be awesome.

    It's a pity about that nonstandard keyboard connector... although if the protocol and the KB controller are close enough to the standard XT scheme, perhaps it may be feasible to devise a cheap adapter for other XT keyboards?
    I've seen references on this forum of people building adapters, so I'm hoping someone has any suggestions on pinout, as I'm super confused after putting a scope and multimeter on things --
    1. I'm pretty sure I've found the 0V and 5V lines, but the 5V line puts out 3.7V when nothing is connected, and after some kind of handshake with the keyboard, it jumps to 4.8V.
    2. All the other lines (presumably reset, clock and data) are at 4.8V constantly. Pressing keys on the keyboard doesn't drop these lines, nor do I see any pulse trains one way or another.
    3. I went through all combinations of these lines I could think of to an XT keyboard through a DIN plug, but with power connected to another XT keyboard, the voltage is 1.2V (and the Corona machine complains no keyboard is connected).
    4. During my probing / testing, with the original keyboard connected, only once, did I see a "6" showing up on the display.

    My less than educated guess -- since I'm not familiar with keyboard protocol and workings, beyond some reading I did yesterday, is that the keyboard controller on the mainboard is probably ok (how else would I have seen a 6?), but something is wrong with the keyboard itself. And I've probably missed a combination of pins with an XT keyboard connected...

    Incidentally, if it helps, it's a Key-Tronic keyboard, model 2402-41. Haven't found much on those online. But I have found some 2402-58s online that seem to come with a DIN plug. Not sure how different these guys are... Still googling! Hoping it's just a different connector, and not a completely different protocol, etc...

    Oh, and if you know how to find the character ROM (would it be readable in memory space?, if not, if it's socketed, I should be able to read it out on my EPROM burner -- what am I looking for on the board?)

  3. #13

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    I think I just figured out why the keyboard isn't working ...

    Ugh.. Ordered foam pad replacements from Texelec...

    20200522_141320315_iOS (2).jpg

  4. #14

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    Quote Originally Posted by VileR View Post
    Nice!
    Well, if you're willing to dump the contents of the character generator ROM (and have a way to do it), that'd be awesome.
    Just found this site -- Maybe that has the ROMs you need?
    https://sites.google.com/hageseter.com/retro

  5. #15

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    Quote Originally Posted by rvdbijl View Post
    I think I just figured out why the keyboard isn't working ...

    Ugh.. Ordered foam pad replacements from Texelec...
    Oh, nice - hope that works out! (and if it doesn't, the BIOS dump in the link you've found might conceivably have more clues about how the machine expects the keyboard to communicate.)

    Quote Originally Posted by rvdbijl View Post
    Just found this site -- Maybe that has the ROMs you need?
    https://sites.google.com/hageseter.com/retro
    Those appear to be the ROMs that are mapped into the CPU's address space: the WD HDD controller at C800h, and the BIOS at F000h.

    The character generator ROM indeed isn't memory-mapped. It should be a 8 KB/64 Kbit ROM, hopefully socketed; I've seen some systems where it's helpfully labeled "CHARGEN" or similar, although that's not very common... but perhaps those other ROMs would be labeled to help distinguish that one.

    Tried looking through the available pictures, videos and diagrams, and unfortunately I couldn't spot exactly where it is. That system unit looks pretty cramped, so if getting to the chip is too much of a hassle, don't worry about it -- I just think it'd be a cool addition, since I already have the one from the PPC-400 (slightly different), and both of them had very nice text displays for that era.
    int10h.org :: :: :: blog

  6. #16

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    I looked around, but there wasn't any obvious ROM in there beyond the BIOS that I saw. I'll take another peek next time I crack the case open. May need to remove the tube to get to the rest of the mainboard..... No guarantees.

  7. #17

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    Yeah, please don't try any surgery if you deem it risky... I'll try to check with the guy who provided the dump from the PPC400, hopefully the innards are similar enough.

    There's actually a much easier method - I've been known to successfully work off of a simple photo of the screen (did that several times for this project), but getting one would require a working keyboard, or some way to write a boot disk. So hopefully those foam pad replacements can fix your keyboard issues.
    int10h.org :: :: :: blog

  8. #18

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    Quote Originally Posted by VileR View Post
    I'll try to check with the guy who provided the dump from the PPC400, hopefully the innards are similar enough.
    Here are his photos. The character set is actually on two 4kB MBM2732A EPROMs (data is interleaved).

    They are the bottom two here: https://int10h.org/dump/PPC400_char_roms.jpg
    Location on the mainboard: https://int10h.org/dump/PPC400_board1.jpg, https://int10h.org/dump/PPC400_board2.jpg

    So if the PPC-21 is anything like the 400, that unfortunately puts them just under the CRT...
    int10h.org :: :: :: blog

  9. #19

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    Quote Originally Posted by VileR View Post
    Here are his photos. The character set is actually on two 4kB MBM2732A EPROMs (data is interleaved).

    They are the bottom two here: https://int10h.org/dump/PPC400_char_roms.jpg
    Location on the mainboard: https://int10h.org/dump/PPC400_board1.jpg, https://int10h.org/dump/PPC400_board2.jpg

    So if the PPC-21 is anything like the 400, that unfortunately puts them just under the CRT...
    Yup, I think I located them. Definitely below the CRT. Not sure if I'm daring enough to pull the CRT out... You did say there was another method if I could interact with the machine? A suggestion from someone on a Facebook forum was to touch the contacts on the keyboard with my fingers -- that seemed to work this morning, so I've been able to try a few things already. Do you need me to take a close-up picture of a full character set on the screen? That I should be able to do.

  10. #20

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    Okay, definitely no need to mess with the tube then. Those things are pretty much irreplaceable these days, as two different shipments have recently taught me (the hard way), so I wouldn't ask anyone else to risk theirs!

    A suggestion from someone on a Facebook forum was to touch the contacts on the keyboard with my fingers -- that seemed to work this morning, so I've been able to try a few things already. Do you need me to take a close-up picture of a full character set on the screen? That I should be able to do.
    Cool, that'd be great. I'll contact you via PM about that to avoid derailing this thread any further, though...
    int10h.org :: :: :: blog

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