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Thread: Booting from an external floppy on a model III

  1. #1

    Default Booting from an external floppy on a model III

    Hi

    Is there a way to boot from the external floppy interface on a model iii?

    I have a hxc floppy emulator and would like to boot from it without having to swap cables. Preferably, I'd like to be able to switch between booting from the internal and external interfaces.

    Thanks

  2. #2
    Join Date
    Jun 2015
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    Sioux Falls SD
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    I know of no way to boot directly from the external floppy. If you are using LDOS 5.3.1, you can boot from the internal floppy and then assign another drive to be the system drive. This is typically used to boot to a hard disk, but it can be done on a floppy, too. But both the internal Drive 0 and the external drive have to be running the same version of LDOS.

  3. #3

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    Quote Originally Posted by mrthreeplates View Post
    Is there a way to boot from the external floppy interface on a model iii?
    Yes, sort of.

    ... without having to swap cables.
    Oops. That was the way.

    Preferably, I'd like to be able to switch between booting from the internal and external interfaces.
    All the ROM knows how to do is load and execute track 0, sector 1 of drive 0.

    You could burn your own ROM that scans the keyboard and then loads and executes track 0, sector 1 of drive 0, 1, 2, or 3 according to which of the '0', '1', '2', or '3' keys is depressed (defaulting to 0).

    But what happens after the sector from drive 2 starts executing? It will likely try to load further data from the disk it came from, but it will do so by executing instructions to load data from drive 0.

    The only way you can really be able to switch between having two different drives as the boot drive is to "swap cables", or install a physical switch that does the swapping.
    -Alan

  4. #4

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    Thanks, yes that is what I was thinking as well.

    My current thought is that I'll pull u6 from the floppy controller and replace it with a custom board. I'll have a switch that will flip the drive select lines making the change transparent.

    Now I just have to make the mini board, and I'm a sw guy!

  5. #5

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    someone create a way to switch between drive 0 and drive 1, maybe you can adjust it to use drive/Gotek ? forget author name its not me, but its called Switch Select Floppy drives in a TRS-80 model 3 or Model 4.pdf
    here is the document on a download link from my cloud storage page https://myaccount.dropsend.com/share...#91;]=15734433

  6. #6
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    Jun 2015
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    Quote Originally Posted by Patrick Bureau View Post
    someone create a way to switch between drive 0 and drive 1, maybe you can adjust it to use drive/Gotek ? forget author name its not me, but its called Switch Select Floppy drives in a TRS-80 model 3 or Model 4.pdf
    here is the document on a download link from my cloud storage page https://myaccount.dropsend.com/share...#91;]=15734433
    This would work if the OP was willing to replace one of the internal drives with the HXC emulator. The internal and external drives are wired differently on the controller board. The first external drive is selected as Drive 0, and not Drive 2.

  7. #7

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    Thanks for the link to that document! That is an interesting approach that I hadn't thought of, much appreciated.

  8. #8

  9. #9
    Join Date
    Jun 2013
    Location
    Melbourne, Australia
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    153

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    I never did get around to implementing my proposed solution. I didn't want to modify my FDC.

    Quote Originally Posted by mrthreeplates View Post
    My current thought is that I'll pull u6 from the floppy controller and replace it with a custom board. I'll have a switch that will flip the drive select lines making the change transparent.
    It sounds like you're thinking of the same thing as me.

    Another idea I was thinking about was to build two long custom flat cables. One would connect to the top of the FDC (which is for drives 0 & 1) and run out to the bottom of the Model III. The second cable would connect the two internal floppy drives and also run out to the bottom of the Model III. You'd connect the two cables together (externally) if you wanted to use the internal drives as normal. Or you could connect the first cable (FDC) to the HxC if you wanted to use that instead. You could also potentially connect the second cable (internal drives) to the external connector so they could be used as drives 2 & 3. You'd have to work out suitable connectors at the external ends of the cables. It would be messy but it would avoid needing to modify the FDC or keep opening the case to swap the cables.

  10. #10

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    Hi Gonk23, Trash-Eighty,

    Thanks! I've ordered parts from digikey to prototype a breadboard so I don't have to do any rework on the floppy controller itself. I'll just have to socket u6 (at least on my version of my model 3's floppy controller). I am going to try to use a 74157 as a mux to make the switching simple. It is going to be a tight fit, so we'll see how it goes. Should be fun.

    I'll report back my progress with pictures.

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