(20S and 21S) RPN Simulator
06-08-2017, 01:03 PM
Post: #1
 Eddie W. Shore Senior Member Posts: 1,251 Joined: Dec 2013
(20S and 21S) RPN Simulator
This program will allow the user to simulate RPN (Reverse Polish Notation) for five arithmetic functions: addition, subtraction, multiplication, division, and exponentiation (power). All operations take the form of enter Y, press [INPUT], enter X, [XEQ] (appropriate key).

Labels:
XEQ A: Y + X
XEQ B: Y – X
XEQ C: Y * X
XEQ D: Y/X
XEQ E: Y^X
XEQ F: “clears” the stack.

The result shown in the display while the X value is left in the hidden display, which can be accessed by pressing [ LS ] (SWAP).

The key codes for the HP 20S and HP 21S are the same.

Code:
 STEP    CODE    KEY 01    61, 41, A    LBL A 02    21, 0    STO 0 03    51, 31    SWAP 04    21, 75, 0    STO+ 0 05    22, 0    RCL 0 06    61, 26    RTN 07    61, 41, B    LBL B 08    21, 0    STO 0 09    51, 31    SWAP 10    21, 65, 0    STO- 0 11    22, 0    RCL 0 12    32    +/- 13    21, 0    STO 0 14    61, 26    RTN 15    61, 41, C    LBL C 16    21, 0    STO 0 17    51, 31    SWAP 18    21, 55, 0    STO* 0 19    22, 0    RCL 0 20    61, 26    RTN 21    61, 41, D    LBL D 22    21, 0     STO 0 23    51, 31    SWAP 24    21, 45, 0    STO÷ 0 25    22, 0    RCL 0 26    15    1/X 27    21, 0    STO 0 28    61, 26    RTN 29    61, 41, E    LBL E 30    21, 0    STO 0 31    51, 31    SWAP 32    14    y^x 33    22, 0    RCL 0 34    74    = 35    21, 0    STO 0 36    21, 26    RTN 37    61, 41, F    LBL F 38    71    Clear 39    71    Clear 40    61, 26    RTN

Example:

In the following examples, 8 will be stored in the hidden register.

7 + 8: 7, INPUT, 8, XEQ A. Result: 15
7 – 8: 7, INPUT, 8, XEQ B. Result: -1
7 * 8: 7, INPUT, 8, XEQ C. Result: 56
7/8: 7, INPUT, 8, XEQ D. Result: 0.375
7^8: 7, INPUT, 8, XEQ E. Result: 5,764,801
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