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Thread: Atlantis MCG-85

  1. #21
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    Nothing.

    Tried 2400, 1200, 300.

  2. #22
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    No activity at all on the TX line, huh? That's not good.

  3. #23
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    I kind of get the feeling (and admittedly, it's only a feeling) that the computer is essentially good. This was a new in package machine, no abuse. And we've got good clock signals, response to reset, etc. Maybe we have a bad IC in there but I would say balance of probabilities is we're flying blind without a manual and just don't really know what it needs. I think finding documentation is really the only way to know for sure if this is a problem with the board or just user error.

  4. #24
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    Well, the first thing is to dump the EPROM. These have been known to go bad.

    Otherwise, the design is straightforward, at least from the standpoint of design. You have an 8085 (known quantity), and 8155 (Timer+256 bytes SRAM) and some EIA interface ICs (MC1488 and MC1489) and a bit of addressing logic (probably a 74LS138; I can't make out the part number on the IC).

    So no mystery at all, at least from the standpoint of electronics and programming. The 8085 was interesting in its own right as you could build a 3 chip functional device with it--and indeed there have been several boards that did just that.

    Much of the expansion stuff is unpopulated, so you can remove that from consideration.

    So basically, with the 8085, you have a complete system with a little ROM and some RAM. The 8155 furnishes the RAM; the EPROM gives you the ROM.
    Serial I/O is easy: Here's an Intel appnote on that from 41 years ago.

    I suppose the 8155 might be bad, so you'd have no RAM, but that's only a distant possibility. Even without RAM, you could still do a "Hello World" program.
    Last edited by Chuck(G); August 18th, 2018 at 12:58 PM.

  5. #25
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    My steps to get something going on unknown 8085-based board:

    * Flash a LED on the SOD pin, very short program that can be all ROM (no RAM required)
    * Flash a LED on the SOD pin, but do a CALL/RET after setting up sthe stack pointer (tests RAM, more of the internal pathways)
    * Light a LED on the SOD pin based on input from the SID pin
    * Print characters to the serial I/O device (in your case, this is bit-bang serial)
    * Echo characters on the serial I/O device
    * Get a ROM monitor up and going (system is fully functional)

    You can use a logic probe on the SOD pin if you don't want to tack a LED on.

  6. #26
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    That Intel app note that I pointed to earlier probably was the basis of more than one SDK, including your Atlantis. Note the baud-rate identification routine. I suspect that, aside from jump and call target addresses that the code in the Atlantis EPROM dealing with serial I/O will be almost byte-for-byte identical to the Intel code.

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