Hi all,
This may be of little interest, but some of you may take advantage of the technique described herein to revive a defeated Fullnut, or getting an OS-free one for M-code experimental purposes.
Saturday afternoon I picked up a non-working fullnut 41C from the post office. Symptoms were somewhat strange. The calculator itself works flawlessly... but, in ALPHA mode, almost every key I press shows a "CAT _" in the display, and even performed a real "CAT (1, 2 or 3)" if I selected it... without leaving ALPHA mode!!!
After some testing with Service ROM, the offending chip was easily identified as ROM-2. It was an "F" version ROM.
Apart from that the calculator was *really* mint. No scratches at all, no markings and no corrosion traces neither external nor internally.
I take the CPU board apart and remove the ROM-2 chip (lower leftmost), obviously no longer "ON" reaction at all...
Then I prepared a modified Clonix to fill the H'2000 page gap with the appropriate Nut2-F.ROM image. Yes, it works!
Next step (I bet you can figure it out) was removing the remaining two ROM chips and configure a new Clonix with the whole Nut OS ROM images for pages H'0000 to H'2000... Yes, it also works!!
Further configs allow me to "play" with different ROM set versions and test "those wonderfull 'bugs'" everyone of us have heard of... but only those fortunate owners on a 19xxAxxxxx have tried... up to now ;-))
I'm *really* far from knowing enough on M-code, so, for me, it isn't anything but a curiosity (and a means by wich I can get a ROM damaged Fullnut back to life). I think a skilled M-code programmer can get a lot of juice out of this "feature"... I may be wrong though.
If there's any interest please let me know.
Best wishes from Spain.
Diego.
Edited: 26 Jan 2004, 9:15 a.m. after one or more responses were posted