IV42 - another calculator for the DM42 hardware

[deetee]

Hello Feierabend!

Thank you very much for trying and testing IV42. Each of your hints are on my ToDoList for the next version.

Some words to your comments:
* Forth offers some kind of 'infinite stack' (memory is cheap these days) - I limited this number to 26 (A-Z). There are differences to regular HP calculators regarding ROT or entering (4x) a constant value to the stack. On the other hand you can use more than 4 registers for programs running or use PICK or STKS (sum up stack).

* There is definitely some kind of 'dimensionsless' feeling when viewing graphics (especially when zooming or shifting). But displaying 4 numbers (x/y min/max) will reduce space or cover the graphics. That's why I decided to push the 4 numbers (xmin, smax, ymin, ymax) to the stack when leaving the graphics mode.

* The 'misterious 7 glitch' remains unsolved so far - but I am quite sure this is related to the keyboard buffer system the OS (DMCP) offers. Good for fast number typing but somehow misterious primarily when changing the keyboard reading mode between 'wait for key' (key_pop()) and 'scan key' (sys_last_key()).

The next version has a TEXT EDITOR (using the 3 rows of function keys to simulate a half QWERT-keyboard + left-right-flipping) and runs the LEGENDARY HP-35 ROM (for reminiscence reasons). By the way the last one needs the 'scan key mode' - so leaving HP-35 pushes a misterious 7 to the stack for sure.

My further plan is to integrate a BASIC interpreter - I'm quite far with it.
My wish is to implement MICROPYTHON which is unfortunately far beyond my capabilities - where an excellent coder (fnord) failed (https://forum.micropython.org/viewtopic.php?f=3&t=8156) so far.

Regards
deetee