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Thread: CPM on MDS225 system generation

  1. #1

    Default CPM on MDS225 system generation

    I have a working MDS225 with DD drives
    And a booting CPM 2.2 disk.

    My goal is to tweak the BIOS for different drive mappings, but first I wanted to just
    re-create a booting unmodified CPM to make sure my process is working, and can't.

    I have what I thought was the BIOS source for this system called BIOS21I.ASM
    and it assembles with MAC just fine.
    I believe the last 3 characters "21I" mean this version has drive parameter tables for SBC202 (DD) drives in A:,B:
    then SBC201 (SD) drives in C:,D:, then IOC integrated (SD) drive in E:
    That's indeed how my bootable CPM maps the drives.

    So, my process is the following, and it doesn't result in a bootable disk:

    MOVCPM 62 *
    SAVE 35 CPM62.COM
    DDT CPM62.COM
    IBIOS21I.HEX
    R2D80 <----- according to DR docs for 62k system
    ctrl-C out of DDT
    SYSGEN
    pressing return for memory source, then B: for destination.
    I've also tried SYSGEN2 which is on my CPM disk.

    This does not create a bootable disk.
    Depending upon experimenting with different load bias's and sysgen type
    I get either the monitor prompt, or a blank screen as if it booted but no display or response.

    Anyone have any ideas on this?

    Yes, I'm on the Brouhaha intel-devsys list

    -Roger in Tyler Texas

  2. #2
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    Default

    What does your boot sector code look like?

  3. #3

    Default

    According to page 6 of the CPM 2.2 alteration guide, when I
    DDT CPM62.com
    the boot code, CPM (CCP+BDOS), and the BIOS should be in memory.
    Then I download the new BIOS hex code
    then SYSGEN which writes out memory to B:
    This write should have the known working boot sector.

    Sound right?

  4. #4

    Default

    If I DDT CPM62.COM then SYSGEN it creates a bootable disk.
    If I use SYSGEN2 it does not.

    This tells me 2 things:
    #1 The DDT command is indeed bringing in the BOOT sector code, CPM and the BIOS

    #2 SYSGEN2 is not reading from memory even though it acts like it is.
    SYSGEN2 will work if the source is A: but not memory.

  5. #5
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    Have you dumped your boot sector to see what it looks like?

    I'm going from the original "CP/M Alteration Guide" instructions.

  6. #6
    Join Date
    Mar 2013
    Location
    Chaffee, MO
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    Default

    Ragnarock,
    Here are a couple url's with good information about sysgen vs sysgen2.

    Code:
    http://www.sydneysmith.com/wordpress/2229/cpm22-gen-2/
    http://www.sydneysmith.com/wordpress/2239/is-cp-m-sysgen-safe/
    Larry
    Last edited by ldkraemer; December 24th, 2018 at 10:05 AM. Reason: updated typo

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