Re: Apple IIC unidisk upgrade

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

In article <3urfm4$re0$2@mhadg.production.compuserve.com>,
Michael Gasperschitz  <100255.523@CompuServe.COM> wrote:
> Who can tell me the procedere for the unidisk upgrade, especially
> which jumpers have to be solderered and or  desoldered when 
> replacing the rom.

There are two mods involved: cut W1 (above and to the left of the ROM)
and solder W2 (between the IOU and MMU).  These mods are required to
allow the use of a larger ROM in the IIc.

Note: once these mods have been made, the original ROM won't work
reliably.  You can make a double copy of the orignal ROM in a 27C256
and use that.

> I have a rom here but I think it is bigger  than the original rom.
> Which is the eprom equivalent to these roms 2716? 2732? 2764?

The original IIc ROM is 16k (27C128 equivalent).  The UniDisk 3.5
compabile ROM is 32k (27C256 equivalent). 

This mod is only needed if you are going from ROM version 255 as
reported by PEEK(64447) to ROM version 0 or later.

There is little or no benefit in using ROM versions higher than 0 in
the original IIc motherboard.  The main feature of the newer versions
is support for the memory expansion card, and the original motherboard
doesn't have a slot for one.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand