The RL-H series of pocket computers represented Panasonic's entry into the so-called HHC, or Hand Held Computer, market. This computer/calculator has a number of interesting/unusual features, such as its universal expansion port (to which either a single peripheral or a peripheral expansion bay can be attached) or its bottom compartment for optional ROM chips which are standard DIP chips whose pins are wrapped around specially manufactured plastic holders.

The RL-H handheld computers are not programmable by default; they are, however, equipped with the functionality of a basic 4-function calculator with memory. Programmability is achieved by the addition of an optional Microsoft BASIC ROM chip. This version of the BASIC interpreter is very simplistic; to my amazement, I found that it doesn't even have trigonometric functions!

Having obtained a compatible printer that connects to this unit, I was dying to find out how one can print results, or list programs, from within the BASIC interpreter. Using the printer was easy in calculator mode; once the printer was turned on through the I/O menu, all calculations were printed automatically. Not so in the BASIC interpreter. Early enough I found out that the interpreter recognizes the syntax print#n where n, presumably, is the identifier of an open file or device; however, for all acceptable values of n (0..15) the device responded with an I/O error. Attempts to open a file resulted in a syntax error.

Lacking any documentation for the BASIC interpreter, I decided to do some reverse engineering instead. I wrote a little program to list the contents of the calculator's memory, in the hope that I'll be able to locate the interpreter's keyword table in ROM:

10 INPUT A
20 PRINT A; TAB(6);
30 FOR I=A TO A+15
40 X= PEEK (I)AND 127
50 IF X<32 THEN X=32
60 PRINT CHR$(X);
70 NEXT
80 A=A+16
90 GET X$
100 PRINT
110 GOTO 20

With the help of this program, I was indeed able to locate the interpreter's keywords, among them the attach keyword. In many BASIC implementations, this keyword was used to open a device for input or output. Next question was the proper syntax of this command; after a lot of experimentation, I found out that attach 29 to #3 does the trick. Afterwards, I can use print#3 or list#3 and obtain output on the printer. (The printer still needs to be turned on through the I/O menu first.)

With the printer at hand, it was much easier to experiment with other programs, including my favorite programming example, the Gamma function. Here is yet another variant of this algorithm, written for the Panasonic HHC. (Note that the precision used in the code is probably an overkill, since this Microsoft BASIC does not perform double-precision arithmetic.)

10 DATA 76.18009172947
20 DATA -86.50532032942
30 DATA 24.01409824083
40 DATA -1.23173957245
50 DATA 1.208650973866E-3
60 DATA -5.395239384953E-6
100 INPUT X
110 T=1
120 IF X>=0 THEN GOTO 160
130 T=T*X
140 X=X+1
150 GOTO 120
160 G=1.00000000019
170 FOR I=1 TO 6
180 READ P
190 G=G+P/(X+I)
200 NEXT I
210 G= LOG (2.506628274631*G/X)
220 G=G-X-5.5+LOG (X+5.5)*(X+.5)
230 PRINT EXP (G)/T