sslee@polyslo.CalPoly.EDU (Steven Lee) (04/29/91)
I'm finally thinking about getting the TOS 1.4 ROMS, however I would still like to get access to the old TOS 1.0 ROMS I have now. (Yes, there are some programs I have that insist on TOS 1.0.) Anyway, what I would like to do is add a simple switch to flip between the ROMS. Sounds easy, right? I'm sure others have done something like this and could fill me in on the details of what problems I may encounter. Thanks, Steven
dth@cs.brown.edu (Dzung T. Hoang) (04/30/91)
In article <281c4c3e.26ba@petunia.CalPoly.EDU> sslee@polyslo.CalPoly.EDU (Steven Lee) writes: > >I'm finally thinking about getting the TOS 1.4 ROMS, however I would >still like to get access to the old TOS 1.0 ROMS I have now. (Yes, >there are some programs I have that insist on TOS 1.0.) > >Anyway, what I would like to do is add a simple switch to flip between >the ROMS. Sounds easy, right? I'm sure others have done something >like this and could fill me in on the details of what problems I >may encounter. > >Thanks, >Steven I propose a solution: Program both TOS ROM sets into 27512 ROMs and use the MSB of the address to select between TOS versions. This would involve programming TOS 1.0 into the bottom (or top) half of the '512 ROMs and TOS 1.4 into the other half. Pin 1 of each 27512 can be used to select the TOS version. 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. ---------------------------------------------------------------------------- Dzung T. Hoang dth@cs.brown.edu ----------------------------------------------------------------------------
adamd@rhi.hi.is (Adam David) (05/05/91)
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)