Re: Misc questions

[RKFAIRCLOTH@unca.edu (Rhonda K. Faircloth)]

In <59fsqs$igk@darla.visi.com> nathan@visi.com writes:

> >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. 

I believe that the old ROM was 16K, while the new ones were 32K. The
difference between the two is minimal, electrically speaking. The 16K 
ROM would have one extra "useless" pin which would likely be pulled up
to +V. On a 32K ROM, that "useless" pin would be an additional address
line, it'd have to be disconnected from +V and routed to a respective
signal on the MMU or motherboard or elsewhere.

 _Apprentice_  |  My folks went to a shaolin temple and
               |  all they got for me was this lousy pebble.