TNC2.12
To complete the task, with NOVRAM bank 0 selected, initialize
the TNC from EPROM.  Set all parameters as desired and PERM them. 
Repeat this process with NOVRAM bank 1 selected, set parameters,
and PERM again.  Now you may select between firmware revisions by
simply setting the NOVRAM bank select switch and hitting reset.

Acknowlegements:  I would like to extend my thanks to the TAPR
hardware team (notably Lyle Johnson) for providing the answer
already on the board, and to the TAPR software team (Margaret,
Harold and Dave) for bringing packet radio to the masses.  I would
also like to thank Ron Raikes, WA8DED, for writing an independent
version of the firmware, which supports multiple connects, and has
a radically different user interface, and provided the firmware
which now resides in my bank 1.