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From: adamd@rhi.hi.is (Adam David)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: TOS ROM switch
Message-ID: <3107@krafla.rhi.hi.is>
Date: 4 May 91 17:36:00 GMT
References: <281c4c3e.26ba@petunia.CalPoly.EDU> <73937@brunix.UUCP>
Organization: University of Iceland
Lines: 22

In <73937@brunix.UUCP> dth@cs.brown.edu (Dzung T. Hoang) writes:
[about making TOS switch-configurable between 1.0 and 1.4]
>The 27512 has the same pinout as the 27256 except for pin 1, so the existing
>ROM sockets can be used, except that pin 1 of each '512 needs to be bent
>90 degrees and soldered together and connected to a switch from either
>+5V or GND.

Rather than bending the pins, it must be simpler to cut the PCB traces to
pin 1 of the 28-pin sockets. This only works for a 6-chip ROMset. IMHO it is
better to make a change that requires the soldering iron to be wielded once
instead of every next time the chips might need changing.
The same idea of an upper and lower bank could be used to make a 2-chip set
on 2-Mbit EPROMS containing 2 different versions (only works on 32-pin sockets).
Another possibility is to use 2 or 3 different 2-chip ROMsets, one in each
pair of sockets. This would appear to be the most common and simplest solution.

On the other hand, I believe there is a disk-bootable version of TOS 1.0
which is legal to run on any Atari ST. If TOS 1.2 is not needed and memory
large enough, this might be the way to go.

--
Adam David.  (adamd@rhi.hi.is)