Synthetic Programming

[Jim Horn]

For the HP-65 and -67, there were several tricks, though the term "synthetic programming" only came along with the '41 due to the rich field of options it had in that regard.

One was NNNs: Non-Normalized Numbers. Each digit was represented as binary coded decimal (BCD). The additional values of 10-15 could be used to make text strings are were used on the '67 for "Error" and such (if I recall, the six values of A-F appeared as "rCodE(space)".

Also, if the mantissa was not normalized, i.e. the most significant digit was zero, instructions that did a divide would take longer as they involved multiple subtractions. By creating the proper value, programmable delays or count down / up timers could be created.

Like the '41, the '67 had a larger address and instruction space than was normally used. By getting the program counter out of the normal program space, you could create almost any bit pattern desired and store it on cards - thus the cards mentioned above. This was initially done by deliberately glitching the card reader, later with the use of a "black box" which plugged into the charging port, and later still with a "phase 0 interrupt" button. My poor '67 was subjected to all the above indignities.

The ability to create almost any bit pattern on cards with a '67 led to the exploration of the '41, ultimately resulting in Bill Wickes' remarkable discoveries of Synthetic Programming on that marvelous machine.

On the '65, there was no program or subroutine counter / pointer (!). Instead, programs were stored in a dynamic shift register. Instructions were coded as six bit values. Two such values represented the program counter and the return pointer. If a second program counter or subroutine pointer were created, all hob could be created - check out the "Rhapsody in Space" article(s) in the old 65 User Notes, circa 1976 (cf. Jake Schwartz disks).

The old 65 User Notes (and later PPC Journal) covered all this in detail. Back when the Web was on paper, the over 5000 members eagerly awaited each one...

Do have fun!