Re: 3.5" UniDisk on a IIc

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

In article <ggonter-2904962125540001@vtr-sta111.ramp.together.net>,
Geof Gonter <ggonter@together.net> wrote:
> Can anyone tell me the last IIc that needed and motherboard update to use
> a 3.5" UniDisk?

It isn't a motherboard update, just a ROM update.


There are three main motherboard revisions for the IIc (not counting
the IIc+, which I'll treat as a separate computer for the purposes of
this discussion).

- the original IIc motherboard
- the revised motherboard which fixes the serial port problem
- the motherboard with the memory expansion slot

There is no easy way to identify which motherboard you have, but you
can usually narrow it down by checking the ROM version.

There are four ROM revisions (again, not counting the IIc+).  You can
find out which ROM your IIc has by getting into BASIC and typing PRINT
PEEK(64447).  I've indicated the number reported for each version.

Version   Description

255       The original ROM.  UniDisk 3.5 is not supported, and there
          is no self-test or mini assembler.  Drive 2 can be booted
          using PR#7.  Mouse firmware is in slot 4.

0         The "UniDisk" ROM.  UniDisk 3.5 is supported, and the self-
          test and mini-assembler are available.  Slot 7 has rudimentary
          AppleTalk support (requiring a nonexistant external interface
          box).

3         The "Memory Expansion" ROM.  The mouse firmware is in slot 7,
          and the memory expansion firmware in slot 4.

4         Bug fixes in the support for the memory expansion card.

All ROM versions will work in all motherboard versions, but memory
expansion support obviously requires the slot which was added in the
last motherboard.

Upgrading from ROM version 255 to version 0 or later requires making a
simple modification to the motherboard: cutting an "X" point and
soldering across a pair of pads.  This must be reversed if go8ing back
to version 255.


Except in very rare circumstances, if your IIc reports that it has ROM
version 3 or 4, you almost certainly have the last motherboard
version.  If you have ROM version 255 or 0, you might have either of
the first two ROM versions, depending on when your IIc was
manufactured and whether the ROM was upgraded.

The only way to be sure of the motherboard version is to open up the
IIc and look for distinguishing features.  The memory expansion slot
is under the keyboard, but telling the first two versions apart also
requires taking out the disk drive and looking for a crystal (or is it
an oscillator?) in place of a chip on the motherboard at location C7.

> I used to have the number (When I had mine updated in 1988) but lost
> it .

In theory, the upgrade offer expired at least a year ago.  The number
"ODL660" comes to mind, but I can't remember if it was for the UniDisk
ROM or the motherboard upgrade.

You should be able to buy the ROM from Alltech Electronics, if they
haven't run out.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand