Recall Arithmetic: The haves and have-nots

[PANAMATIK]

It is interesting, that the non programmables HP-45, HP-27 does have recall arithmetics, and the programmables HP-55,HP-65,HP-97,HP-25,HP-29C don't have it.

The reason for it is, that the necessary one byte opcodes for program steps were not available. RAM space was very precious and program steps were coded as one byte to get a maximum of 98 steps (HP-29C) or 224 steps (HP-97) from the RAM chips. The storage arithmetics in HP-29C needs 64 opcodes of 256 possible, and the recall arithmetics would have needed another 64 opcodes, which were not there.

see the list of program step opcodes http://panamatik.de/ProgramCodes.pdf.

The later generation programmables HP-32S, HP-42S used at least >8 bit opcodes to solve this problem.

Bernhard