Re: Misc questions

[david@wraith.cs.uow.edu.au (David E A Wilson)]

nathan@visi.com (Nathan Mates) writes:
>In article <59fi12$1ou@balsam.unca.edu>,
>Rhonda K. Faircloth <RKFAIRCLOTH@unca.edu> wrote:
>>Anybody out there have a description
>>of what needed to be done to the motherboard so it would accept the newer
>>(double in size of the older) ROM? I'm not as interested in the serial
>>timing fix, but it wouldn't hurt. :)

>   If there's larger ROMs, you need a place to put them (or probably
>larger pinouts unless you multiplex). The MMU (Memory Management Unit,
>but doesn't do any forms of protected memory) may also need some extra
>functionality to do rom bankswitching; not sure if Apple's engineers
>thought ahead or not. 

The original //c had a 27128 equivalent ROM while the later models used
a 27256. Both these chips have the same number of pins and all that needs
to be changed when swaping ROM sizes is to cut/solder the two jumpers J1 & J2
(one is a bow-tie and is cut, the other is two semi-circles and is soldered).

If you have a really old motherboard this will not fix the serial port speed.

My //c (dead) has the old ROMs but the retrofitted clock for the serial chips.
-- 
David Wilson	Dept CompSci Uni Wollongong Australia	david@cs.uow.edu.au