# HP Calculator Wiki

### Site Tools

20b:software-4banger

## Software framework

### Description

A simple framework that implements a simple programmable RPN calculator. The keyboard mapping is still based on a 20 key 4-banger I designed a while back. The output is based on the 20b's screen.

The framework is designed to be easily expanded to include extra functions.

The current keyboard layout is shown below. Some things are a bit non-intutive (GSB . is GOTO; GSB 0 is RTN) but this part of the code will need to be completely revised once a proper layout for the 20b has been designed.

### Keymap

Character to keyboard mapping:

  enter   v       c       backspace
7       8       9       /                q = quit
4       5       6       *                t = trace mode
1       2       3       -                f = status
0       .       space   +                ^L = redraw screen

Non-shifted keys

  ENTER^  X<>Y    CHS     Clx
7       8       9       /
4       5       6       *
1       2       3       -
0       .       shift   +                  

Shifted keys:

  LASTx   Rv      EEX     CLREG/CLPRG
n!      sqrt    1/x     PGRM
ln      e^x     y^x     SST
STO     INTG    TEST    R/S
RCL     PI      shift   GSB