HELP
Contains help file(s) for built-in DM42 help that can be activated from main system soft menu by
pressing
[
F1
]
key (leftmost in top row of keys).
OFFIMG
Bitmap files from this directory are displayed when the calculator is turned off. See
OFF Images
chapter for more details.
PROGRAMS
Raw files with programs are loaded/saved from/to this directory.
SCREENS
Screenshots of calculator LCD are saved into this directory. See
LCD Screenshots
for more
details.
STATE
Calculator state files with extension .s42 are stored in this directory. See chapters
Load State
or
Save State
how the load or save calculator state.
Calculator Extensions
Virtual variables
Managing some of the new features specific to the DM42 is something that spurred a lot of
discussion. Initially we wanted to re-purpose some of the so-called "reserved" flags of the HP-42S
but it soon became apparent that others had already done so in various patches for Free42 and we
wanted to avoid trampling on anybody’s toes with our own patches for Free42.
The next idea was to extend the number of flags available beyond 100 but obviously only have
them accessible via indirect addressing as there was no question of patching Free42 to accept 3
digits in the various flag instructions. But then, how do we make integer values (and one real value)
available to programs without assigning a whole block of flags that are going to be awkward to
read?
After that we thought of using extended register numbers. They would either have to be assigned
ridiculously high index numbers in order to avoid conflict if someone decided to go for a register
array SIZE of 2000, or they would have to be assigned negative index numbers. We couldn’t use
negative indexes because the HP-42S and Free42 just take the absolute value of the index and use
that to access the correct register and some programs might rely on that.
We settled on the concept of "Virtual Variables". These are variables that do not (and cannot, for
that matter) exist in the DM42’s variable table. Because of this, they are not listed in the variable
menu when you press RCL or STO but there is a way to make them easy-ish to access, just read on…
There are six such virtual variables:
"DevID"
2
