Sharp PC-1201

---

By the mid-1970s, most Japanese pocket calculators were made from domestic parts; from 1974, scientific calculators built with Japanese chips also appeared. The next milestone was the programmable pocket calculator, which was no longer developed using American circuits, but manufactured using domestic technologies. So these first models did not even resemble their American siblings: the Casio PRO-101 four-function programmable calculator, which was completed by the end of 1975, and its successors, which have been expanded with scientific functions a year later: the fx-201P, and its twin, the fx-202P with non-volatile memory, and the PRO fx-1 with magnetic card reader, have an unusual programming model, which have been developed based on the computers’ Fortran programming language, while Sharp's domestic model PC-1200 and the export model PC-1201 in 1977 feature an easier-to-use keystroke-programming method. Initial attempts did not bring the expected success at first, but the development of dot-matrix liquid crystal displays three years later allowed Sharp to create the truly easy-to-program EL-5100 and the world’s first pocket computer, the PC-1211.

The Sharp PC-1200/1201 models, of course, bears some resemblance to competing Japanese models, but its programming model is completely different: it has a 128-step program memory, 12 user-accessible data registers; the entered program can be easily checked from the display, but the usability of the machine is increased mostly by program-editing capabilities, and keystroke programming model, i.e. entering a program is identical to performing similar calculations manually. The entered program is not lost even when the calculator is switched off, as the memory circuits are continuously powered by two extra button cells.

Using the calculators

The calculator can operate in three modes, which can be set with the upper slide switch on the right:

• the CAP mode is used to delete the entered program,
• in PRO mode you can enter, check or edit the program,
• while the RUN mode can be used to perform manual calculations and running the program.

In PRO mode, the format of the display is similar to that of american-made programmable machines: the number on the left shows the program counter, i.e. the number of the current program step; and the right side shows the instruction code — or codes — stored in that location. These instruction codes are generated basically from the row and column number of the corresponding key, meaning that the first digit is the row number (1 to 8) on the keyboard, and the second digit is the column number (1 to 5).

The numeric keys have their own value (00..09), and the shift key F has an F letter. The corresponding key sequences always occupy a single program step, their display consists of up to three numbers or the letter ’F’. For example, the instruction code for the F x=t 2 key sequence is F-75-02.

The program is entered in the same way as the keys pressed for manual calculations; however, the display shows the number of the next program step instead of the result of the calculation.

The calculator has 12 data registers, which can be accessed with the digits 0 to 9, and s and t keys. The results can be stored in these registers by pressing x→M, the contents of these registers can be displayed with RM, the number can be added to these registers with M+ and pressing the register identifier as mentioned above. All data registers can be cleared by pressing F CAM.

Each program or part of a program can be labeled by pressing F LBL and an identifier (0 .. 9, s or t). The individual programs or if necessary, the parts of the program has and ’end of program’ instruction, which can be placed with the S/E key. The unconditional jump to each label can be programmed by pressing GTO and the corresponding identifier. Labeled program sections are also available as subroutines and can be called by pressing F GTS and the corresponding identifier. At run-time, the subroutine returns to the main program when reached an END command programmed with S/E. The calculator does not allow nested subroutine calls, i.e. subroutines cannot call another subroutine.

There are four conditional instructions for conditional branching of the program, which compare the number stored in register x with registers 0, or ’t’: F x&neq;0, F x<0, F x&eq;t and F x<t. If the specified condition is true, execution continues by jumping to the label specified as part of the statement; if it is false, the program continues with the next instruction. For example, F x<t s jumps to the program section marked with F LBL s if x is less than t. The machine beeps when a comparison with the ’t’ register has resulted true. It is not possible to call subroutines with conditional jump instructions.

The program can be edited in PRO mode. Use the CA key to go to the beginning of the program, the FST key to go one step forward, and the BST key to go back one step in the program. Since the display always shows the currently entered instruction when entering the program (i.e. the display always shows the previous instruction), an incorrect keystroke can be corrected accordingly: after displaying the incorrect program step, it is necessary to press BST before pressing the correct key.

Similarly, a program step can be inserted with the INS key is placed after the displayed step. For example, the INS key pressed when the display shows 002 F-43 will move steps 003 and beyond by one, the newly inserted blank statement will be placed in step 003.

Unnecessary program steps can be deleted with the F DEL key sequence, which deletes the displayed program step and placed any further instructions one position backwards.

The entire program can be deleted in CAP mode by pressing the CA key. It is important that deleting does not work in RAD mode.

The program run can be suspended with the HLT instruction, which is suitable for requesting variables and displaying results. In this case, a HALT symbol appears on the display at run-time, which shows as a small letter ’u’. In this case, the program can be resumed by pressing the S/E key.

In RUN mode, calculations are performed manually in the same way as for other scientific calculators. The program always starts where the program counter points. The program counter is reset with the CA key, so it is suitable to jump to the beginning of the program. The program can be started from a specific program label, which can be accessed by pressing the GTO and the key corresponding to the given identifier.

When debugging, it is useful to run the program step by step: pressing the FST key will execute the next instruction and then stop running.

Here is an example of a factorial calculation program:

Step	Keying	Instruction(s)
000	x->M t	55-83
001	1	01
002	x->M 0	55-00
003	x->M s	55-82
004	F LBL 0	F-13-00
005	RM s	65-82
006	×	54
007	RM 0	65-00
008	=	84
009	x->M s	55-82
010	1	01
011	M+ 0	75-00
012	RM 0	65-00
013	F x<t 0	F-85-00
014	RM s	65-82
001	S/E	85

To run the program, switch to PRO mode:

CA S/E, entering the number, then S/E. The machine beeps according to iterations, then the result displayed, and program is stopped.