From: ddkilzer@iastate.edu (David D Kilzer)
Subject: Re: //c and Apple 3.5 drive
Keywords: //c, 3.5" drive
Organization: Iowa State University, Ames, IA
Date: Fri, 16 Oct 1992 20:18:01 GMT

In article voss@i40s16.ira.uka.de (Stefan Voss Betr.Kilger) writes:
>Herbert Fung writes
>> I tried to hook up my Apple 3.5 drive to my friend's //c but I can't seem 
>> to get it to work. I tried PR#5 but it didn't work. PR#7 turned on the 
>> light but didn't read or boot the disk. The eject button didn't even 
>> work.
>> Help?
>
>You don't mention what kind of 3.5" drive you tried. Normal Apple 800k 3.5"
>drives, AMR 3.5" drives and AE 3.5" drives can't be hooked up to an //c !
>The only 3.5" drive that works with a //c is the Apple 3.5" UniDisk, but
>I'm not sure if you can boot from the UniDisk. 

Yes, you can boot from the Unidisk.  However, you must not put a disk in
the 5.25" drive, or else the //c will try to boot from it.  The //c
scans from slot 7 to slot 1 looking for drives to boot from.  The 5.25"
disk is in slot 6, the 3.5" disk in slot 5.  Therefore, you must not put
anything in the 5.25" drive if you want to boot from the 3.5" disk.
NOTE:  This is ONLY if you want to cold-boot (turning on the computer)
or warm-boot (using ctrl-oa-reset) the computer.

If you're in BASIC, for example, a PR#5 will boot the 3.5" disk
directly, and you don't have to worry about having a disk in the 5.25"
drive.

One final note.  If you do, in fact, have an Apple UniDisk 3.5" (as
opposed to the plain Apple 3.5" drive) and you have it connected to the
//c correctly and it STILL does not work, there is a reason: a certain
version of the //c ROM won't work with the UniDisk 3.5" drive.

To find out which //c ROM version you have, go into BASIC (or if you
don't have a disk handy, just turn on the computer and hit ctrl-reset
after you see the "Check disk drive." message) and type the following
line and hit return at the "]" prompt:

PRINT PEEK (64447)

If you get the number "255", then you have the original //c ROMs, and
should go to your nearest authorized Apple Dealer and get your //c logic
board swapped for free (bring your UniDisk 3.5" drive with you, along
with any of its receipts, to verify that you actually HAVE one).  I
believe Apple still honors this free swap, which corrects the problem of
not being able to use the UniDisk 3.5" drive with the //c.  You should
get the "3.5 ROM //c", which PEEK (64447) = 0.

NOTE: ONLY PERSONS WHO HAVE PROOF OF OWNING A //c (with Original ROMs)
AND A UNIDISK 3.5" DRIVE MAY GET THE LOGIC BOARD SWAP FOR FREE.  Please
don't go to your Apple dealer and ask for the swap if you don't have a
UniDisk 3.5".

Values of the PEEK (64447) are as follows:

255   Original //c ROM                   (Can't use UniDisk 3.5")
  0   3.5 ROM //c                        (CAN use UniDisk 3.5")
  3   Original "Memory-expandable" //c   (CAN use UniDisk 3.5")
  4   Revised "Memory-expandable" //c    (CAN use UniDisk 3.5")

  5   Apple //c+  (built-in 3.5" drive; can use Unidisk 3.5" AND Apple 3.5")

For those of you who might be interested in other differences between
//c ROM versions, see Apple // Tech Note #7 for the Apple //c.

Dave
-- 
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