On Sat, 15 Dec 2012, joshbensadon wrote:
> --- In firstname.lastname@example.org, 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
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
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
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/