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Thread: Atari 520STm External Floppy Drive

  1. #1

    Default Atari 520STm External Floppy Drive

    Quote Originally Posted by Fooser View Post
    I've found a Samsung SFD-321B and modded it for DS0. I also built a external drive cable based on this discussion: http://www.atari-forum.com/viewtopic.php?t=26656.
    The drive was modded based on this: http://www.atari-wiki.com/index.php/...D_Floppy_Drive

    I found this post elsewhere in the forum:

    Quote Originally Posted by fatwizard View Post
    I have modified a standard PC 3.5" floppy drive to work in my ST. The drive needs to be set as drive 0, or the first drive, instead of the typical drive 1 setting for PC drives. Also, the disk change line needs to be connected to pin 2 of the floppy interface instead of it's usual connection to pin 34. Some drives have jumpers for these changes, but most later day floppy drives don't. They do, however often have jumper pads on the circuit board that can be used to reconfigure the drive

    I modified this drive (a TriGem, made by Samsung) by removing a zero ohm resister connecting the DC signal to pin 34, and soldered in a jumper wire to connect the DC circuit to pin 2 of the floppy interface connector. I then removed a solder bridge that jumpered the drive to be drive 1, and bridged the adjacent connection to address the drive as 0...
    Since I'm using a custom cable, do I need to make the DC signal modification?
    - Don Mankin -

    [
    TRS-80 Models I, 4, 4p, Coco 2, 100, 102. Tandy 1000 RLX. Osborne 1a.
    At
    ari 800, 520 STm. Commodore 64.
    Amiga 1000. TI-99/A. Sinclair ZX-81]

  2. #2
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    Atari doesn't care about DC, but you may want to change pin 34 to READY (per the OEM manual for the Samsung drive). I'm not certain that the 520 requires it, but it wouldn't hurt if it doesn't.

  3. #3
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    The floppy drive will work without the DC line, but you have to be careful to close any windows to the disk that are open before you eject the disk or corruption can occur, or so I have read. I have a small utility for the ST that confirms the operation of the change line (DC).

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    In particular, here's the pinout of the floppy connector.

    One
    and another

    In short, there's nowhere for either a READY/ or DC/ pin to go. DC didn't really come along until late 720K and early 1.44M floppies. READY/ was more the rule, following the 360K/720K 5.25" floppy drives.

  5. #5
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    I'll be dipped! Looks like I tediously modified a couple of PC floppy drives for no reason. I obviously never looked for the DC or ready lines in the pinout diagrams. I have read repeatedly about the function of the DC line for the ST, I even collected a little utility that verifies the change disk detection called MEDIAC.TOS. I just dug that program out, and ran it on the 520ST I am currently playing with, and when you eject the disk, it reports that "The disk may have been changed". I noticed this time it says "may have been", like it's not sure. I wonder how it works?

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    One can monitor the write-protect line without starting the spindle motor. With the spindle motor energized, one need only check for the presence of an INDEX pulse.

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