*In addition to registers 00-19, the following registers may be available: 60-69 (corresponding to the machine's operation stack); 70-97 (mapped to program steps 0-223); and 98-99 (can be used without restrictions; not erased by the CMs key)

The SR-52 was Texas Instrument's first programmable calculator, and represented this company's answer to the Hewlett-Packard HP-65. When it was introduced in 1975 or thereabouts, it was a true electronic marvel. It was also probably one of the thickest and heaviest pocket calculators ever made.

The calculator has 224 program steps and 20 memory registers. (A few additional registers, as well as some other undocument features, are available to the enterprising programmer.) A built-in magnetic card reader (with a really huge motor inside) provided the ability to record and play back programs. One side of a card held 112 program steps, so a single card was sufficient to store the contents of the entire program memory. The calculator was also compatible with the PC-100 printer/security cradle.

The calculator had all the features of a state-of-the-art key-programmable machine, including register arithmetic, conditional branching with multiple test conditions, flags, and a decrement-and-skip function. With the exception of the 2nd key, program steps were not merged; each keystroke occupied one program step in program memory, so for instance, RCL 0 0required three program steps of storage.

Back when I first held one of these one pounders in my hand, I'd have given an arm and a leg to own it. I now own two vintage units and in one of them, I even managed to get the 25-year old card reader to work! Somewhat unreliably, but it does read and write cards. Long ago, I acquired the habit of always creating at least one, perhaps two backups when I write a magnetic card, so I usually end up with at least one working copy. Sadly, the other unit's card reader appears to be permanently damaged. I believe an optical sensor inside is damaged due to battery outgassing, so the reader doesn't correctly detect it when a card passes through, nor does it detect the presence of the write-enable sticker.

The following program is an implementation of the Gamma function for this machine. It is interesting to compare this program with that written for the HP-97. Both machines have 224 program steps, but whereas the SR-52's are unmerged, the HP-97's are fully merged. The result is a program that's almost 50% longer on the SR-52, despite the fact that the polynomial has been rearranged and optimizations specific to the algebraic logic of Texas Instruments calculators are used to reduce the number of program steps needed.

To use the program, enter the function argument and hit the A button. The program calculates the Gamma function value for any real argument except for negative integers.

000 46	LBL
001 11	A
002 65	×
003 01	1
004 42	STO
005 00	0
006 00	0
007 46	LBL
008 80	IFP
009 95	=
010 80	IFP
011 41	GTO
012 49	PRD
013 00	0
014 00	0
015 85	+
016 01	1
017 41	GTO
018 80	IFP
019 46	LBL
020 41	GTO
021 42	STO
022 00	0
023 01	1
024 65	×
025 53	(
026 02	2
027 65	×
028 59	π
029 54	)
030 30	√
031 85	+
032 93	.
033 08	8
034 06	6
035 07	7
036 06	6
037 00	0
038 04	4
039 03	3
040 04	4
041 02	2
042 04	4
043 85	+
044 08	8
045 03	3
046 95	=
047 65	×
048 43	RCL
049 00	0
050 01	1
051 85	+
052 93	.
053 09	9
054 02	2
055 06	6
056 04	4
057 09	9
058 04	4
059 07	7
060 09	9
061 85	+
062 01	1
063 01	1
064 06	6
065 08	8
066 95	=
067 65	×
068 43	RCL
069 00	0
070 01	1
071 85	+
072 93	.
073 02	2
074 04	4
075 05	5
076 02	2
077 09	9
078 07	7
079 00	0
080 05	5
081 85	+
082 08	8
083 06	6
084 08	8
085 07	7
086 95	=
087 65	×
088 43	RCL
089 00	0
090 01	1
091 85	+
092 93	.
093 02	2
094 09	9
095 05	5
096 01	1
097 04	4
098 07	7
099 07	7
100 85	+
101 03	3
102 06	6
103 03	3
104 00	0
105 08	8
106 95	=
107 65	×
108 43	RCL
109 00	0
110 01	1
111 85	+
112 93	.
113 06	6
114 02	2
115 07	7
116 08	8
117 09	9
118 05	5
119 02	2
120 85	+
121 08	8
122 00	0
123 09	9
124 01	1
125 06	6
126 85	+
127 07	7
128 05	5
129 01	1
130 02	2
131 02	2
132 93	.
133 06	6
134 03	3
135 03	3
136 01	1
137 05	5
138 55	÷
139 43	RCL
140 00	0
141 01	1
142 95	=
143 55	÷
144 01	1
145 44	SUM
146 00	0
147 01	1
148 43	RCL
149 00	0
150 01	1
151 55	÷
152 01	1
153 44	SUM
154 00	0
155 01	1
156 43	RCL
157 00	0
158 01	1
159 55	÷
160 01	1
161 44	SUM
162 00	0
163 01	1
164 43	RCL
165 00	0
166 01	1
167 55	÷
168 01	1
169 44	SUM
170 00	0
171 01	1
172 43	RCL
173 00	0
174 01	1
175 55	÷
176 01	1
177 44	SUM
178 00	0
179 01	1
180 43	RCL
181 00	0
182 01	1
183 55	÷
184 53	(
185 43	RCL
186 00	0
187 01	1
188 85	+
189 01	1
190 95	=
191 65	×
192 93	.
193 05	5
194 44	SUM
195 00	0
196 01	1
197 43	RCL
198 00	0
199 01	1
200 45	yx
201 53	(
202 43	RCL
203 00	0
204 01	1
205 75	-
206 05	5
207 95	=
208 23	lnx
209 75	-
210 43	RCL
211 00	0
212 01	1
213 95	=
214 22	INV
215 23	lnx
216 55	÷
217 43	RCL
228 00	0
229 00	0
220 95	=
221 81	HLT