HP-25 Emulators suggestion

[Valentin Albillo]

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Hi, Namir,

(02-06-2024 04:51 PM)Namir Wrote:  For anyone out there who has and will implement HP-25 emulators, how about ading GSB and RTN commands using line numbers at least? There are aviable shift keys for these two commands on the HP-25 keyboard.

You asked the very same question about the HP-12C in another thread. It's not a question of available locations on the keyboard, Namir, it's a question of available keycodes.

In both the HP-12C and the HP-25, each programmable instruction occupies one byte, i.e. one keycode of the 256 available. If you were to add GSB to any of those machines you'd need 50 keycodes for GSB 01 to GSB 49 (HP-25) plus RTN, and you simply do not have that many available, only 16 are unused as Teenix just said.

This is also the reason why on the HP-12C, even though there are 20 data registers available (R0 to R9 and R.0 to R.9) (Owner's Handbook p.24) Storage register arithmetic (STO+, STO-, STOx, STO/) is possible with only registers R0 to R4.

Why ? Because there aren't enough keycodes available for R5 and beyond, let alone for GSB 01 to GSB 99. On the other hand, the HP-15C programmable instructions (700 in all) can use one or two bytes of program memory and this solves the problem of keycode availability.

Regards.
V.