If you _need_ to use functions from both modules in a
program, and you reach a program step where you want
to enter the name of a function which exists in _both_
modules, then:
Turn the HP-41 off.
Take out one of the modules - keep only the one
whose function you want plugged in.
Turn the HP-41 back on, enter program mode, put
the function you want into the program. Since only
one module is plugged in, there is no conflict.
Now you can carry on entering the program. When you
need to, turn the HP-41 off and put in the other
module.
Although the function _names_ are the same, the
program steps actually contain an XROM command,
which will be different, depending on which module
was plugged in when the program step was entered.
When you run the program, both modules can be plugged
in and the program will still work.
Things are less clear-cut if you try to execute a
function whose name is in both modules, from the
keyboard - the function is picked from the module
in the lower-numbered port. To override this, assign
the function to a USER mode key, with only the module
you want plugged in. The command will then work when
you press that key even if both modules are later
plugged in.
The worst-case scenarion is where different functions
have the same XROM number! But that's a different topic.
Keep those HP-41s working!
Wlodek Mier-Jedrzejowicz