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 row and column on the keyboard. For example, the ENTER↑ key on the HP-65 would be code 41. All codes that don't start with 0 obey this rule. On the HP-97, keys on the right keypad were given codes beginning with −.
A number. All codes starting with 0 represent the corresponding number. For example 04 means the 4 key.

The HP-55 had an exception to the above rules. GTO was displayed as a minus (−) thus GTO 25 would display as −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 ↑	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	↓	45	Print/Space	65	Ln x
06	6	26	Enter Exp	46	End	66	To Rect
07	7	27	↑	47	Continue	67	Hyper or x ←()*
10	8	30	x⇄y	50	If x = y	70	Sin x
11	9	31	Roll ↓	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	e^x
15	f	35	÷	55	\|y\|	75	Log x
16	c	36	×	56	π	76	√x
17	d	37	Clear x	57	Pause	77	Sub* or Return*

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