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Thread: Want to replace an old 1/2 height 3.5" FDD - need pinouts for the 26 pin connector

  1. #1

    Default Want to replace an old 1/2 height 3.5" FDD - need pinouts for the 26 pin connector

    Hi there,
    I have just acquired an old KAWAI Q-55 Sequencer which has an internal 1/2 height 3.5" FDD and uses 720Kb 2DD diskettes - probably late '80s vintage
    It actually works, but since it had not been used for years, the grease in the platter bearing is hardened and it does not spin up reliably ( the belt slips due to the resistance ). The connector cable is 26 pins at approx 1.25 mm pitch.
    I have a working Samsung SFD-321S Slimline FDD which is also 26 pins, but much more recent.
    Please could anyone provide the pin assignments for the early drive? ( I suspect it may be similar to a Citizen OSDA-53B or earlier )
    So what I am hoping is that someone has an old manual with the pinouts for an equivalent FDD. I believe there was an IBM standard for the early 26 pin FDDs.
    Once I have some data I can make up a cable to splice the new FDD 1 mm pitch ribbon to the old.
    Thanks

  2. #2

    Default

    here is pinout for the old 26 pin drive:

    Pin Pin
    Name Description
    1 VCC VCC +5V
    2 /INDEX Index
    3 VCC VCC +5V
    4 /DRVS Drive Sel
    5 VCC VCC +5V
    6 /DSKCHG Disk Change
    7 RES Reserved
    8 READY
    9 MEDIA
    10 /MOTE Motor Enable
    11 /REDWC Density Select
    12 /DIR Direction
    13 RES Reserved (Inuse)
    14 /STEP Step
    15 GND Ground
    16 /WDATE Write Data
    17 GND Ground
    18 /WGATE Write Gate
    19 GND Ground
    20 /TRK00 Track00
    21 GND Ground
    22 /WPT Write Protect
    23 GND Ground
    24 /RDATA Read Data
    25 GND Ground
    26 /SIDE1 Side 1 Select



    and here's the newer 34 pin:

    ^^^ 34 min male connector


    ^^^ 34 pin female connector

    Pin Name Dir Description
    2 /REDWC --> Density Select
    4 n/c Reserved
    6 n/c Reserved
    8 /INDEX <-- Index
    10 /MOTEA --> Motor Enable A
    12 /DRVSB --> Drive Sel B
    14 /DRVSA --> Drive Sel A
    16 /MOTEB --> Motor Enable B
    18 /DIR --> Direction
    20 /STEP --> Step
    22 /WDATE --> Write Data
    24 /WGATE --> Floppy Write Enable
    26 /TRK00 <-- Track 0
    28 /WPT <-- Write Protect
    30 /RDATA <-- Read Data
    32 /SIDE1 --> Head Select
    34 /DSKCHG <-- Disk Change


    Floppy Diskdrive pinout (Shugart interface):
    Pin Name Dir Description
    2 /DCD --> Disk Change Detect
    3 Key no pin in this position
    4 /DS3 Device Select 3. Not sure but Amiga 500"s schematics reveal that this signal might be used for motor control of internal DF1: on the Amiga 2000
    6 /INUSE A common open-collector LED driver signal? I have never seen this signal used anywhere.
    8 /INDEX <-- Index
    10 /DS0 --> Device Select 0
    12 /DS1 --> Drive Sel B
    14 /DS2 --> Device Select 2
    16 /MTRON --> Motor On
    18 /DIR --> Direction
    20 /STEP --> Step
    22 /WDATE --> Write Data
    24 /WGATE --> Floppy Write Enable
    26 /TRK00 <-- Track 0
    28 /WPT <-- Write Protect
    30 /RDATA <-- Read Data
    32 /SIDE1 --> Head Select
    34 /RDY --> Drive Ready
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    Fake86 8086/V20 PC emulator: http://sourceforge.net/p/fake86
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  3. #3
    Join Date
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    Location
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    Default

    Pins 10 to 16 of the 34 pin interface are a little confused; MotorOn & DS A & B refer to the PC interface and twisted cable, not the drive. The Shugart list has it right, although 0, B and 2 are also a little confusing. 10, 12 and 14 select the first, second and third drive respectively (0/1/2 or 1/2/3, per the maker's whim), and 16 turns on the motor (unless it is jumpered to turn on automatically with DS or InUse, optional on some drives).

    Good luck!

    m

  4. #4

    Default

    if he does have problems spinning the motor, i know this would be really ghetto but it could just be made to spin all the time by feeding that line 5 volts... i think?
    My emulators!
    Fake86 8086/V20 PC emulator: http://sourceforge.net/p/fake86
    MoarNES Nintendo emulator: http://sourceforge.net/p/moarnes


  5. #5
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    Default

    Quote Originally Posted by Mike Chambers View Post
    if he does have problems spinning the motor, i know this would be really ghetto but it could just be made to spin all the time by feeding that line 5 volts... i think?
    --------
    Connecting 5V to any of the control or signal lines is *NOT* a good idea since you would quite possibly damage the interface driver on the controller or the drive!

    *Grounding* pin 16 will turn on the motor on most drives; if it's the only drive you could also connect pin 16 to the drive select (probably pin 10 or 12 in this case).

    Since most of them are connected to more than one drive, disk drive signals are almost always the open-collector variety, i.e. the transmitting end has a switch that either shorts it to ground (true) or leaves it disconnected (false) while the receiving end has a resistor to +5V to pull it up to 5V when all the transmitters (which are connected in parallel) are open-circuit. Obviously, connecting 5V to a line which is connected to ground through a driver IC will not be good for that IC. On the other hand, grounding any of the signal lines will not cause any harm.

    But I suspect any 26 vs 34 pin incompatibilities are more likely to be with the Ready, DiskChange and Density signals.

    m

  6. #6

    Default Looking good ! thanks for the prompt info

    here is the comparison table of the old to new drive pinouts ...
    pin___Old Drive____________________New drive
    ===============================================
    01 __ VCC VCC +5V ________________ VCC
    02 __ /INDEX Index _______________ INDEX
    03 __ VCC VCC +5V ________________ VCC
    04 __ /DRVS Drive Sel ____________ DR0
    05 __ VCC VCC +5V ________________ VCC
    06 __ /DSKCHG Disk Change ________ DSKCH
    07 __ RES Reserved _______________ N/C
    08 __ READY ______________________ N/C
    09 __ MEDIA ______________________ N/C
    10 __ /MOTE Motor Enable _________ MTR0
    11 __ /REDWC Density Select ______ DRVDE0
    12 __ /DIR Direction _____________ DIR
    13 __ RES Reserved (Inuse) _______ N/C
    14 __ /STEP Step _________________ STEP
    15 __ GND Ground _________________ GND
    16 __ /WDATE Write Data __________ WRITE DATA
    17 __ GND Ground _________________ GND
    18 __ /WGATE Write Gate __________ WRITE GATE
    19 __ GND Ground _________________ GND
    20 __ /TRK00 Track00 _____________ TRACK 0
    21 __ GND Ground _________________ N/C
    22 __ /WPT Write Protect _________ WRPRO
    23 __ GND Ground _________________ GND
    24 __ /RDATA Read Data ___________ RDATA
    25 __ GND Ground _________________ GND
    26 __ /SIDE1 Side 1 Select _______ SEL


    I will make up a cable and have a play. The worst that can happen is that I may need to do a couple of pull ups.
    I will let you know how it goes.

  7. #7
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    I hesitated about posting this but your Kawai reference triggered some vague recesses of my memory. I have an old Roland PR100 Sequencer. It takes 3" or 3 !/4" floppies as I disappointedly found out. In researching the disks used ISTR some reference to Kawai disks being compatible. I also found a dealer who supplied them, but for the uses I could put the Roland to the prices were way out of line. Now perhaps that is a later model Kawai or my memory banks are scrambled, but have you tried inserting a 3.5 floppy in the drive ?

    Lawrence
    Economics isn't a real science. It's an evil art designed for the rich.

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