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Thread: Amiga High Density pin 2

  1. #1
    fletch31337's Avatar
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    Default Amiga High Density pin 2

    Hi.

    Been studying Amiga and PC floppy drives recently.

    One thing has got me scratching my head.

    On a PC with a high density floppy drive, pin 2 on the internal floppy connector is used to signal to the PC whether the floppy disk inserted is a double density or high density (known as /REDWC or "Density Select").

    Obviously, when a high density disk is inserted, the hole in the disk prevents the internal switch being pushed and thus a high density disk is "selected". Conversely, when a DD disk is inserted, there is no hole, so the switch is activated and therefore a double density disk is "selected" (not sure which one sets /REDWC to a high or low signal, but it doesn't really matter for this conversation).

    However the Amiga is very close to the original Shugart interface and pin 2 is /DCD (Disk Change Detect).

    So what I'm trying to figure out is: When using an Amiga high density drive like an FZ-357A or FB-357A, how does the Amiga know what density disk is inserted? Obviously the density select switch in the drive is connected to something, but how is this signalled to the Amiga when pin 2 is not available for /REDWC?

    Any thoughts welcome!

    Regards,

    Fletch.

  2. #2
    timfelgentreff's Avatar
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    Default

    I cannot find the source right now, but I think density select on Amiga was done via the identifying pulses that the drive sends initially (via the RDY signal, IIRC).

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