I have made an assembler and simulator in Javascript, (I modified the assembler-simulator from Marco Schweighauser).

The simulator includes a calculator display and keys. You can download it from the file list, or try it online at: www.enscope.nl/rrca

The first program is a 8-digit calculator that can only add. You can paste the following code in the online assembler, assemble it and start the simulator.

; CPU simulator test. 
; Only calculates:  A + B =

 NOP ;first instruction is skipped !
clr:
plus:
  LDL Y,X	; save X in Y (32 bit)
  SUBL X,X	; clr X  (32 bit)

waitkey:
  HLT ; wait for button press
;  HLT ; option for switching to single step

  TEQ CL,'+'
  BRZ plus
  TEQ CL,'='
  BRZ result
  TEQ CL,' '  ;  CLR pressed ?
  BRZ clr
  ADD CL,0xffd0 ; keep digit code (subtr 0x30)
  ADDL X,X ; shift X one digit left
  ADDL X,X
  ADDL X,X
  ADDL X,X
  ADD XL,CL ; add new digit at the right side
  BR waitkey
  NOP        ; delay slot: the instruction after BR is also executed !

result:
  DADDL X,Y  ; 32-bit decimal add (Decimal ADD Long)
  BR waitkey

The architecture document was changed on a few minor points: The name of a few instructions changed, and the position of some bits in the opcode changed. There are a few new instructions in the above code that are not yet in the documentation: HLT and NOP.

After a calculation, press the "clr" button before a new calculation is started.

Change the code and build your own calculator online ! You can also use scientific notation: two digits of CL are displayed as exponent, and the upper bits in CL control minus-signs and a decimal point after the first digit.

The page does not save your modified code, so you have to do some copying.