Writing about the FX-501P calculator has been a long overdue task of mine. It was, after all, considered at one time a true competitor in a field of machines characterized by such marvels as the TI-59 or the HP-41C. With the FX-501P, Casio established itself as one of the few truly serious players in this highly competitive field.

The FX-501P is one of the most sophisticated calculators made during the brief era of "yellow LCDs", liquid crystal displays characterized by the yellow UV filter designed to protect early, unstable liquid crystal compounds from the UV component in sunlight and flourescent office lighting. But the color of the display is not the only thing that distinguishes the FX-501P from later calculators, including its more advanced cousin, the FX-601P.

A genuinely unique feature of the FX-501P is its ability to generate music. Yes, that's right! The calculator's designers must have been in a playful mood when they decided that its compatibility with an externally attached cassette recorder can be used for a dual purpose: not only to record data, but also to record electronic music. The machine even comes with a keyboard overlay template that is designed to make it easier to "compose" a musical "program". Unique? You bet!

But there's a great deal more to the FX-501P than such prehistoric gadgetry. It is also a quite capable scientific programmable, with 128 fully merged program steps, 10 memories, and a comprehensive programming model that even includes indirect addressing capability. In fact, the FX-501P's programming model is essentially identical to that of the FX-601P, with one exception: keycodes, rather than alphanumeric key mnemonics, are used for program display.

To demonstrate this machine's programming capability, here again is my Gamma function example, complete with keycodes:

001	C6-00	Min00
002	   01	1
003	C6-01	Min01
004	   05	5
005	C6-0F	MinF
006	F0-01	LBL1
007	C7-00	MR00
008	FF-06	x>=F
009	F1-02	GOTO2
010	C7-00	MR00
011	   E1	×
012	C7-01	MR01
013	   E5	=
014	C6-01	Min01
015	   01	1
016	C9-00	M+00
017	F1-01	GOTO1
018	F0-02	LBL2
019	C7-00	MR00
020	   E1	×
021	   F9	ln
022	   E4	-
023	C7-00	MR00
024	   E3	+
025	   C0	(
026	   02	2
027	   E1	×
028	   EE	π
029	   E2	÷
030	C7-00	MR00
031	   C1	)
032	FF-c6	√
033	   F9	ln
034	   E3	+
035	   C0	(
036	   C0	(
037	   C0	(
038	   C0	(
039	   09	9
040	   09	9
041	FF-C8	1/x
042	   E2	÷
043	C7-00	MR00
044	FF-C7	x2
045	   E4	-
046	   01	1
047	   04	4
048	   00	0
049	FF-C8	1/x
050	   C1	)
051	   E2	÷
052	C7-00	MR00
053	FF-C7	x2
054	   E3	+
055	   01	1
056	   00	0
057	   05	5
058	FF-C8	1/x
059	   C1	)
060	   E2	÷
061	C7-00	MR00
062	FF-C7	x2
063	   E4	-
064	   03	3
065	   00	0
066	FF-C8	1/x
067	   C1	)
068	   E2	÷
069	C7-00	MR00
070	FF-C7	x2
071	   E3	+
072	   01	1
073	   C1	)
074	   E2	÷
075	   01	1
076	   02	2
077	   E2	÷
078	C7-00	MR00
079	   E4	-
080	C7-01	MR01
081	   F9	ln
082	   E5	=