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28723Re: [midatlanticretro] Re: New 8" system works (was Lobo floppy drives)

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  • Mike Loewen
    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:


      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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