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Re: New 8" system works (was Lobo floppy drives)

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  • joshbensadon
    ... Thanks Mike, I did not know that. Would you happen to know more about what the DS drive does with two index hole sensors? Like does it merge them into
    Message 1 of 40 , Dec 15, 2012
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      --- In midatlanticretro@yahoogroups.com, Mike Loewen <mloewen@...> wrote:

      > It's not the density that matters, but single or double sided. The
      > index hole aperture in an single-sided 8" disk is in a different location
      > than on a double-sided disk. Double-sided drives will typically have two
      > index hole sensors: one for single-sided and the other for double-sided.
      >


      Thanks Mike,

      I did not know that. Would you happen to know more about what the DS drive does with two index hole sensors? Like does it merge them into the single index pulse on the 50 pin? Is a new pin used for the 2nd sensor? Or is there a new pin used to tell the controller it's a DS disk?

      Cheers,
      Josh
    • Mike Loewen
      ... Here s the service manual for the Tandom TM-848, with the schematics in the back: http://bitsavers.trailing-edge.com/pdf/tandon/TM848_service_1982.pdf
      Message 40 of 40 , Dec 15, 2012
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        On Sat, 15 Dec 2012, joshbensadon wrote:

        > --- In midatlanticretro@yahoogroups.com, Mike Loewen <mloewen@...> wrote:
        >>
        >> The double-sided drives have a 2S signal on pin 10 of the interface
        >> connector to indicate single or double-sided media. The outputs of the
        >> respective pulse-shaping ciruitry for each sensor is essentially ORed to
        >> form a single Index pulse output.
        >
        >
        > Cool, so I can imagine the two sensor signals going to an RS flip flop
        > to provide the 2S signal and as you said to an OR gate for the index.

        Here's the service manual for the Tandom TM-848, with the schematics in
        the back:

        http://bitsavers.trailing-edge.com/pdf/tandon/TM848_service_1982.pdf

        Knock yourself out. :-)

        > Hmm, thinking about why, I guess the design was to create a hardware
        > error if a user placed a DS disk into a SS drive. As Rich found, the
        > lack of index pulses caused a drive not ready. Correct me if I'm wrong,
        > but in later 5.25" drives, they did not change the index sensor
        > location. Then I suppose the errors created would be software
        > generated?

        The 5.25" drives only had a single index hole aperture.

        > I vaguely remember hearing a discussion about how computers switched
        > from hardware solutions to software solutions, then back to hardware.
        > I just don't know the dates, could this 8" to 5.25" be part of that
        > switch?

        I couldn't say. Certainly Woz did a lot in software for his Apple II
        disk controller design. Another odd thing about the 8" drivers vs the
        5-1/4" drives was that the 8" drives had a write-enable notch, while the
        5-1/4: drives had a write-protect notch. Very confusing.


        Mike Loewen mloewen@...
        Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
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