The Museum of HP Calculators


Key Codes

Because the older calculators could only display numbers, each key was assigned a code so that the programs could be read. The code was simple - each number represented either:

The HP-55 had an exception to the above rules. GTO was displayed as a dash (-) thus GTO 25 would display at -25.

The HP-9100A & B don't use this convention. They list their keycodes on the pull-out reference card in their bases. If your card is missing, the keys are:  (* marks codes/keys found only on the HP 9100B. Each of these codes can represent two functions which is determined by context. i.e. a 77 after a GO TO is a Sub not a Return.)
Code Key   Code Key    Code Key    Code Key
00 0 20 Clear 40 y->() 60 Acc+
01 1 21 . 41 Stop 61 Rcl
02 2 22 Roll up 42 Fmt 62 To Polar
03 3 23 x->() 43 If Flag 63 Acc-
04 4 24 y<>() 44 Go To () () 64 Int x
05 5 25 drop 45 Print/Space 65 Ln x
06 6 26 Enter Exp 46 End 66 To Rect
07 7 27 Enter (up) 47 Continue 67 Hyper or
x <-()*
10 8 30 x<>y 50 If x = y 70 Sin x
11 9 31 Roll dn 51 71 Tan x
12 e 32 Chg Sign 52 If x<y 72 Arc
13 a 33 + 53 If x>y 73 Cos x
14 b 34 - 54 Set Flag 74 ex
15 f 35 ÷ 55 |y| 75 Log x
16 c 36 x 56 PI 76 Sqrt
17 d 37 Clear x 57 Pause 77 Sub* or
Return*

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