🚀 go-pugleaf

In article <CMM.0.88.624463452.cmm1@cunixa.cc.columbia.edu> cmm1@CUNIXA.CC.COLUMBIA.EDU (Christopher M Mauritz) writes:
>PC Ditto v3.01 will NOT work with TOS 1.4.  I forget what the error
>says, but I think it was something like: "Does not work with this
>version of TOS" or something to that effect.  Too bad there isn't a way
>to piggy back the two versions of ROMs and have a hardware switch
>between them.

No? Well, the first solution it is easy, if You have a machine with TOS
in 6 ROMs. 

These are xx256 JEDEC-pinout-compatible mask ROMs. So 27256 EPROMS are
possible replacements.

And so are 27512. Pin 1 of the 27256 is called Vpp (programming voltage)
and is to be held at +5Volts when the ROM is simply used (not
programmed).
Pin 1 of the 27512 EPROMs is the necessary additional adress line.

So, get Your EPROM programmer, read in each of Your original ROMs (all
twelve of them), get 12 sockets (28 pin, 600 mil EPROM sockets), a 10
kOhms resistor, a siple litte switch, some isolated wire and 6 27512 (or
C512) EPROMs. 

Remove pin 1 of 6 of Your sockets; this is done to isolate EPROM pin 1
from the ST circurit board. Plug in the remaining 6 sockets. See how pin
1 has lost contact to the +5Volts line. Connect all pin 1 with some wire.

Now connect the 1 kOhms resistor to pin 1 and pin 28 of one of the upper
sockets. Pin 28 is the +5Volts (Vcc) power source for the ROMs.
Connect the wire to the switch and the switch to ground (pin 14 of the
ROMs is ground, for example).

Now the switch switches the most significant adress line for the
512-EPROMs between ground (low) and open (10-k pullup to Vcc; high). So
the switch selects "upper half" or "lower half" of the EPROM.

Burn a set of EPROMS with TOS 1.2 (or 1.0) in one half and Rainbow TOS
in the other.

works fine for me :-)

Second solution: use 6 static RAMs (62256 or Nec42256 and a battery to emulate 6
ROMs.
This was done by some german freak, who published his solution in the
german magazine c't. The pcb is availeble, as are the required PAL
chips. This even adds a Mega-ST-compatible clock to non-Megas...

I'm still trying to find some time to get it to work... :-(

hase
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