Re: Apple IIc ROM 255

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

Mark Percival <mark.REMOVE.percival@videotron.ca> wrote:

> Is the upgrade still available from Apple?

No, but Alltech Electonics <http://www.allelec.com> may be able to
supply you with the UniDisk-compatible firmware update.

> What problems might one encounter with this machine?

There are two major points you should be aware of:

- Motherboard design "feature" which causes problems with some serial
devices, particularly modems.  The only way to fix this is to do a
reasonably major hardware hack or to replace the motherboard.

- You have the original firmware, so your IIc is missing some features.
Here is an extract from Apple IIc Technical Note #7 which summarises the
characteristics of the original (255) and UniDisk (0) firmware versions.

Original IIc ( $FBBF = $FF )

o    Can use the IIc external drive only
o    No AppleTalk firmware
o    PR#7 boots the second drive
o    Mouse firmware maps to slot 4
o    Serial firmware does not mask incoming linefeed characters
o    Serial firmware does not support XON/XOFF protocol


3.5 ROM IIc ( $FBBF = $00 )

o    Can use the IIc external drive and the UniDisk 3.5 drive
o    AppleTalk firmware maps to slot 7
o    PR#7 returns the message "AppleTalk Off Line"
o    Mouse firmware maps to slot 4
o    Serial firmware defaults to mask all incoming linefeed characters
o    Serial firmware supports XON/XOFF protocol

<end of extract>

The following points should be noted:

- The "IIc external drive" mentioned above is the external 5.25" drive.
All versions of the IIc also support the UniDisk 5.25 or Apple 5.25
Drive (but only one can be connected).  You can even use a Disk ][ via
an adaptor.

- The "AppleTalk firmware" mentioned for the revised firmware serves no
useful function.  AppleTalk support was never completed for the IIc, and
this partial implementation was removed in a later revision.

- The UniDisk 3.5, which is supported by the updated firmware, is a
different drive from the much more common Apple 3.5 Drive.  The latter
is the drive normally used with the Apple IIgs, and as the internal and
optional external drive for the Mac SE and Mac II (it also works on the
Mac Plus and several later models).

The UniDisk 3.5 only works on the IIc, IIgs and (with a card) IIe.


Note that if you are considering getting the firmware update, it
involves dismantling the IIc, replacing a single ROM chip, and doing a
couple of minor modifications to the motherboard, both of which are
marked (one cut and one solder blob).

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