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Thread: Attaching a 5 floppy drive to a mid 1990s IBM Thinkpad 760

  1. Default Attaching a 5 floppy drive to a mid 1990s IBM Thinkpad 760

    Hi Guys

    I've been pondering this for a while. These laptops have a 5V TTL floppy connector on the rear, and I'm keen to attach an old Tandon TM100 drive to it.

    Has anyone done anything like this? I've not even been able to find a pinout for this connector, or schematics or any other related information!

    Cheers

  2. #2

    Default

    have you checked the hardware maintenance manual for the pinout?

  3. Default

    Quote Originally Posted by mR_Slug View Post
    have you checked the hardware maintenance manual for the pinout?
    Yes! I did find quite a good service manual for it - no mention of the floppy pinout. I could buy an external drive and crack it open but they are not common in the UK. Would rather not ship one from the US if I can avoid it!

  4. #4

    Default

    Even if you figured out the pinout of the TP760 external floppy drive port, made the appropriate connections to the TM100, and provided an external power supply to accommodate the higher power requirements of the Tandon TM100 - it is likely the TP760's floppy controller (designed for a 1.4M 3.5" drive) would not work with a 360K 5.25" drive.

  5. #5
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    Default

    If said FDC supported reading 720K 3.5" (DS2D) disks in that 1.44M drive, there's not reason that a 360K drive couldn't be used for reading.

    But right now, we have very little information about the system. Not even a schematic or chipset callout?

  6. Default

    Update. After an excruciating (and I am not kidding there) 3 day process of trying to work out the pinout. I made up a MDR26 to DC37 (IBM standard external floppy) cable, and I've got a bog standard 1.44 working as B: drive

    http://xpander.mattmillman.com/files/floppy.jpg

    So... next difficulty. The controller (a standard Super I/O - PC87334) definitely does support all types of floppy (IBM would have had a job finding one that only supported 3.5" drives at that time), but the BIOS doesn't. I kind of expected this.

    The laptop runs NT 4.0 which doesn't use the BIOS to access the floppy, so I've hacked floppy.sys to force B: to be 360K 5 1/4". Now I just need to go get the TM100 from storage and see if it works.
    Last edited by inaxeon; June 3rd, 2020 at 02:37 AM.

  7. Default

    Pinout if anyone wants it. This is for 486 and Pentium I models only. Newer models use a smaller connector which may be different.

    13: (1)
    12: RDATA
    11: (2)
    10: GND
    9: WDATA
    8: DIR
    7: MOTEN
    6: DRSEL
    5: (2)
    4: GND
    3: GND
    2: +5V
    1: GND

    26: DSKCHG
    25: SIDE
    24: WP
    23: TRACK0
    22: WGATE
    21: STEP
    20: (2)
    19: DRATE0 (3)
    18: (1)
    17: INDEX
    16: (1)
    15: (2)
    14: DRATE1 (3)

    1: N/C or Unknown
    2: Mystery connections to a large IBM ASIC. Likely not floppy related.
    3: Unsure as to why these are present on this connector. Not required for drive use.

  8. Default

    Quote Originally Posted by Chuck(G) View Post
    If said FDC supported reading 720K 3.5" (DS2D) disks in that 1.44M drive, there's not reason that a 360K drive couldn't be used for reading.

    But right now, we have very little information about the system. Not even a schematic or chipset callout?
    That is interesting. It read/writes/boots from 720K no problem. I wonder if this quirk may get me *some* functionality from the '3.5" only' BIOS implementation. That'd mean I could potentially boot from 360K - a major bonus.

  9. #9

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    And 1.2Mb 5 1/4", Good job btw

  10. Default

    After experimenting around with this I see that I am getting a lot of read errors.

    Turns out my 80's rubbish bit of Spectra Strip is quite capacitive. I solved it by putting a 1.8K pull-up on RDATA in the DC37 shell.

    Can't wait to try the Tandon, unfortunately I can't get at it till this weekend.

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