Re: //c & 3.5 problem

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <3li2p1$d9q@news.ysu.edu>,
Dirk John Fischer <am883@yfn.ysu.edu> wrote:
> 
> I have a 3.5" Apple external drive that has an 'eject' button on the
> righthand side & an led on the left & a daisy chain port on the back.

Ah, but what colour is it, and what name is written on the underside?

There are three similar 3.5" drives from Apple.

1. The UniDisk 3.5 (white, eject button is thin and mounted above the
   disk slot on the right, manual eject hole is separate and in line
   with the disk slot).

2. The Apple 3.5 Drive ("platinum", eject button is the same height as the
   disk slot and in line with it, with the eject hole in the middle of the
   button).

3. The SuperDrive (looks the same as the Apple 3.5 Drive, except my
   one has a yellow access LED instead of a red one, and there is a
   bulkier plug on the cable).

Of these three types, only the first one can be used on the IIc.

The IIc+ and IIgs can use all three (the SuperDrive will only be able
to access 400k/800k disks, except for a IIgs with a SuperDrive
Controller Card).

The IIe can use all three with an appropriate controller card.


The UniDisk 3.5 is an "intelligent" drive - it has its own 65C02
microprocessor, and transfers formatted packets of data to/from the
computer, with a packet for each block read or write.  SmartPort
commands issued within the computer are passed directly to the drive
for handling.

The Apple 3.5 Drive and SuperDrive are not intelligent - they send raw
data to and from the computer, and it is up to the computer to handle
seeking, sector encoding, etc.  SmartPort commands are handled by the
computer.

Because the UniDisk 3.5 does a lot more work than the Apple 3.5 Drive,
it means the computer has to do a lot less, meaning less firmware is
required, and a slower interface is possible.

The UniDisk 3.5 transfers data to and from the computer at the same
speed as a 5.25" drive (4 microseconds per bit), which is slow enough
for a software loop to handle reading and writing on a standard speed
Apple II.

The Apple 3.5 Drive transfers data twice as fast (2 microseconds per
bit), which is too fast for a 1 MHz Apple II without special hardware
support (as in the IIc+ or the Universal Disk Controller card).  The
IIgs runs in "fast" mode when accessing the 3.5" drive, so it is able
to keep up.

> Now, DAVEX says this about my //c:
> 
> System: Apple IIc version 2: 3.5" disk ROM

What does it mean by "version 2"?  The possible values contained in
the ROM location that identifies the IIc version are 255 (original
IIc), 0 (UniDisk 3.5), 3 (Memory Expansion), 4 (bug fix) or 5 (IIc+).

I expect "version 2" means "second version", i.e. ROM version byte = 0.

> I cannot seem to get anything to recognize the disk drive. If I explicitly
> access 'drive at S5 D2' - a red LED comes on on the drive but I still get a
> 'No Device Connected' error. Also, I have to open the case & manually eject
> any disk I have inserted. The 'eject' button does not depress far enough to
> manually eject a disk. Is this a 'design enhancement'?

The "eject" button does not cause manual eject.  In a UniDisk 3.5, it
is detected by software and the software activates the motorised eject
mechanism.

In an Apple 3.5 Drive, when plugged into a IIgs, IIc+ or
compatible disk port, it triggers the state machine in the drive to
initiate an eject.  With a Mac (or when plugged into an incompatible
disk port), it does nothing.

Both drives have a manual eject mechanism: insert a straightened
paperclip or some other reasonably firm thin metal object into the
eject hole, and press (it takes a reasonable amount of pressure).
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand