Subject: Re: Floppy Interfaces
Newsgroups: comp.sys.apple2
From: dempson@actrix.gen.nz (David Empson)
Date: Sun, 17 Sep 2000 00:34:22 +1200
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Simon Biber <simon@basilisk2.cjb.net> wrote:

> Could this be what you're talking about?:
> "To hook up a UniDisk 3.5" for an Apple //, just take the external drive
> cable from your 400k drive, and plug it into the MECHANICAL ASSEMBLY of your
> UniDisk drive. You MUST bypass the analog card inside the UniDisk to use the
> drive on a Mac. You kinda have to take a lot of the UniDisk apart to get at
> the connector on the mech. assy. This disables the eject button on the
> UniDisk, as well as the LED "in use" light."
> 
> Would this be applicable to the 5.25" drive as well?

No.  This so called "analog card" inside the UniDisk 3.5 is actually a
complete microcomputer, consisting of a 65C02 processor, RAM, ROM and an
IWM disk controller.  The IWM is used for two functions: to communicate
with the host Apple II, and to control the drive (it has a mode toggle).

Once you bypass this card, you have a bare 800K 3.5" drive mechanism
(which has somewhat limited intelligence, but much more than an Apple
5.25" drive), which is exactly the same as the mechanism used in an
Apple 3.5 Drive and a Macintosh 800K drive.  The Mac already supports
this, so nothing more is needed.

By comparison, the Apple 5.25 Drive (or UniDisk 5.25, or Disk ][, or the
//c external 5.25" drive) is a bare drive mechanism plus a real analog
card which controls the mechanism.  It requires precise timing to
control all aspects of its read and write operation (unlike the 3.5"
drive mechanism), and the computer has direct control over the stepper
motor which is used to seek to tracks.  (In a 3.5" drive, the computer
sends rudimentary commands to the drive, telling it to step up or down a
track, for example.)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P O Box 27-103, Wellington, New Zealand