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Thread: MFM Disk Controllers

  1. #1
    Join Date
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    Default MFM Disk Controllers

    G'day Guys. I need to make controllers talk to MFM disks.
    Specifically, a controller currently running a dying 40MB disk, being reconfigured to run a 32 MB disk.
    Years ago I was given a DEBUG procedure to Low Level Format.
    DEBUG (enter)
    g=c800:5 (enter)
    I recall 5 as the Interleave, but I can't remember what g=c800 is.
    ***********************
    Also any info please, on running 2 different capacity hard disks from the one controller.
    Today is the tomorrow u stressed about yesterday.

  2. #2
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    Default

    A long shot - isn't c800 the hexadecimal memory address you will call? I.e. what you do is to execute (g = go) a routine loaded into RAM (or ROM), but what the argument after the colon is, I couldn't tell. If there is no user interface to the controller, maybe a skilled PC (I assume) hacker could disassemble the routine that happens to start at $c800 and figure out if there are some other entry points to reconfigure the controller.
    Anders Carlsson

  3. Default Re: MFM Disk Controllers

    [quote="Rolf"]G'day Guys. I need to make controllers talk to MFM disks.
    Specifically, a controller currently running a dying 40MB disk, being reconfigured to run a 32 MB disk.
    Years ago I was given a DEBUG procedure to Low Level Format.
    DEBUG (enter)
    g=c800:5 (enter)
    I recall 5 as the Interleave, but I can't remember what g=c800 is.
    ***********************

    no ,the "5" is not the interleave , it is the offset of the address
    the command "g=C800:5" means run from the address "C800:5"(it is due to the register of the 8088/8086 is 16 bit but the 8088/8086 could address up to 20bit=1M .)
    all you need to know is the address of bios of your card
    in most case , it is C000,C800 ,......
    if you are sure you have type C800 in this card , just do

    DEBUG (enter)
    g=c800:5 (enter)

    usually it will pop a program and you can configure your card again
    as for setting of two MFM disk , i have not done this before but i have heard a rumor that you'd better use two identical disk esp in an old controller.

  4. #4
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    Default

    Some MFM controllers don't have ll formatting programs, and some have it at a diffeferent address than the c800:5 one. Getting two drives to work together on a single chain usually isn't much of a problem. Just make sure that one is addressed as device 0, and the other is device 1. Also, the last drive on the chain needs a termination resistor block installed, and none on the other one. Then, just daisy-chain the 34-pin cable to both drives, and one of the 20-pin cables to each one. (It makes a difference which 20-pin cable goes to which drive, as they are hard-wired on the controller card to be first drive & second). If one or both drives need to be ll formatted, the ll format program allows you to choose which drive to format. (It'll also prompt you with some other questions that you'll need to know the correct answers to, such as, number of heads, number of cylinders, first cylinder, last cylinder, write precomp, landing zone, and prob'ly a few more which evade me at the moment). Do not attempt to ll format an MFM disk until you have armed yourself with the necessary information.

    --T
    Teach your children how to think, not what, and hold 'em close, not tight.
    _____________________________________________

    Please visit the Vintage-Computer Wiki. Contributers welcome.

  5. #5
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    Default Re: MFM Disk Controllers

    Quote Originally Posted by Rolf
    G'day Guys. I need to make controllers talk to MFM disks.
    I've gone the debug route but Ontrack's DiskManager is much easier.

  6. #6
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    Default Thanx Guys

    Update is the 32MB disk is a Seagate 238R. It's existing controller runs it as a 20MB unit. It is an RLL drive, so I guess now I gotta find a friendly controller. Thoughts please.
    At ur convenience, please checkout the Software Forum re Win v1.01.
    Today is the tomorrow u stressed about yesterday.

  7. #7
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    Default Re: Thanx Guys

    Quote Originally Posted by Rolf
    Update is the 32MB disk is a Seagate 238R. It's existing controller runs it as a 20MB unit. It is an RLL drive, so I guess now I gotta find a friendly controller. Thoughts please.
    At ur convenience, please checkout the Software Forum re Win v1.01.
    I've never tried it but other folks have reported only mixed success in RLL formatting a drive that has been (incorrectly) formatted as MFM. Sometimes they'll come back and sometimes not. Good luck, hope it works out for ya.

    --T
    Teach your children how to think, not what, and hold 'em close, not tight.
    _____________________________________________

    Please visit the Vintage-Computer Wiki. Contributers welcome.

  8. #8
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    Default Re: Thanx Guys

    Quote Originally Posted by Terry Yager
    I've never tried it but other folks have reported only mixed success in RLL formatting a drive that has been (incorrectly) formatted as MFM. Sometimes they'll come back and sometimes not.
    I've gone back and forth with drives. Never had much trouble. (Might take >1 format)

  9. #9
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    Oh, I'll keep that in mind, in case it ever comes up.

    --T
    Teach your children how to think, not what, and hold 'em close, not tight.
    _____________________________________________

    Please visit the Vintage-Computer Wiki. Contributers welcome.

  10. #10

    Default

    Somebody already pointed out that C800:5 is a segment and offset combination. If the drive controller has a BIOS at C800, this was the customary place for the built in formatting routine.

    RLL drives are designed to a higher quality spec than MFM drives. You should be able to run an RLL drive as plain MFM - it's not as strenuous. Formatting an MFM drive as RLL might work, but I would trust the data.

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