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27690NorthStar Horizon Woes

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  • Kyle Owen
    Oct 14, 2012
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      Well, it's been an exciting past few weeks! I was able to get an NEC APC to boot using an 8" drive and some diskettes that someone I work with had. I'm going to get some Pascal going later, as I'm looking forward to seeing the color test program.

      I also managed to find some boot disks for the N* Horizon from the same guy. He had stashed them away from many years ago, and they happened to be in a box of 5.25" floppies (mostly soft-sectored) that he had intended to give me a while ago. Imagine that! 

      What do you know, after playing around with it, it actually boots! I realized that the card placement is actually somewhat important. My understanding is that by placing two cards (processor and floppy controller, for example) at either end of the motherboard, you are terminating the bus. As I understand, this helps eliminate reflections, just like you'd get with an unloaded feedline in the ham radio world. After putting the processor card in the first slot and the floppy controller in one of the last ones, it's now booting from a few of the floppies. 

      I have a 20k SRAM board (EconoRAM 24k, though one 4k bank is unpopulated) and the N* 16k DRAM board. After setting the address of the 16k DRAM board to 0x0000, I am able to actually boot N* DOS. Inserting the EconoRAM board in any slot seemed to make everything wonky and not boot. Removing it solved the problem. 

      I started measuring some voltages on the card, and discovered one 7805 was bad. After replacing it, I found that another one hit the dust. Go figure! I replaced the other bad one, and although it's running really hot, it does seem to work now. I'm sure those 7805s are being pushed to their absolute limits. 

      With 36k of RAM starting at 0x0000, I can boot my N* DOS just fine, as well as my 32k CP/M 2.2 disk. Well, almost. The CP/M hangs up after telling me what it is. I never get to a prompt. I'm thinking I may have the 32k of RAM it needs in not quite the right space.

      I see on just one of my three N* DOS diskettes a monitor program, in this case M0E00. I seem to have the 5.2 DQ edition of N* DOS, which went from the DOS at 0x2000 to 0x0100. I believe the monitor location also changed. However, when I type "GO M0E00", the computer freezes up and must be manually restarted. Also, after playing with the system more, two of my three DOS boot disks have become no longer bootable, though they are still quite readable (at least from an LI command). I wonder what happened there.

      Either way, I don't think I have any way of making some more boot disks unless I can get to the monitor program to manually edit some memory locations. Dave's NST utility can only work if I can put it into RAM, which is either done by using a ROM board, or by using the monitor to edit the utility in RAM.

      Any ideas where I should go from here? I have inserted write-protect stickers in hopes that my last remaining bootable disk will stay that way. I think something was inadvertently wiping track 0 or something. 

      I have one blank hard-sector floppy and would be willing to send it to someone to get a real copy of N* DOS on it. Would anyone be up for that? Assuming I don't have any other issues with my system, like bad RAM, I think it could be a big help.

      I'm going to make another topic regarding my RAM card design. Stay tuned!

      Kyle
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