Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!sun-barr!ccut!wnoc-tyo-news!toumon!wucc!ytsuji
From: ytsuji@wucc.waseda.ac.jp (Y.Tsuji)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: ROM sockets in a Mega ST 2
Summary: DIY or buy a dual TOS plug-in board.
Message-ID: <5547@wucc.waseda.ac.jp>
Date: 29 Apr 91 13:49:31 GMT
References: <1991Apr29.083447.27132@bernina.ethz.ch>
Organization: The Centre for Informatics, WASEDA Univ.
Lines: 23

In article <1991Apr29.083447.27132@bernina.ethz.ch>, 
felner@nessie.cs.id.ethz.ch (Tomas Felner) writes:
> I want to upgrade a friend's Mega ST2 to TOS 1.4. 
(deleted)
> Questions: 
> 
> Why are there 6 sockets if the ROMs only need 2?
So that 6 new ROMs can be placed.
> Or do I have both options,
Yes, you do.
> 2 and 6 ROM chips? If so, how do I change from one to the other? Is there a
> jumper somewhere?
6 ROMs are 256 stuff while 2 ROMs are 1 megabit stuff. You must 'short'
pin 2 and 12 of U12 (pluck off the IC first and replace a socket so that
future TOS can be fitted in 2 chips.) As for jumpers w2 and w3, replace
the caps the other way.
> I would prefer the 6 chips solution. If I have to stick with
> 2 chips, which EPROM type do I need?
The same type you have had of course.
The Best Electronics of San Jose sell a plug-in board by Wizztronics
that looks after two different sets of ROMs( 2 and 2, 2 and 6, or 6 and 6
chips) for $69.95. It will allow you to switch between to different OSes.
I haven't tried it but I can well imagine it.