Clearing Return Stack on HP-15C

[Pekis]

(10-07-2024 03:22 AM)brouhaha Wrote:  Executing a GSB doesn't "stop" when the return stack is full. It just loses the oldest entry.

Aside from doing a RTN when there's only one address on the return stack, there are several things that can explicitly clear the return stack, including CLR PRGM, executing RTN in run mode, and modifying the program (inserting or deleting program steps). I've identified the microcode subroutine that clears the return stack, but I haven't yet figured out the purpose of some of the microcode routines that call it.

Thanks for the explanation !

So, if I understand, once a program is running, it always accepts 7 GSB levels ... but in the worst case, if there is a R/S instruction in the program, just before entering the 8th GSB level (which would have thrown a "ERROR 5"), and then manually do R/S to resume the program execution, the HP15C will never report the problem nor end the program normally... Gasp