HP HP-65 - Page 55

= If a function is executed in a program, execution of
resumes the program.
Program
LEVEL 1 LEVEL 2
Press LBL
A
Resumes calling
program
Resumes calling
program
Stop ] t
= A function executed from the keyboard or a nonfunc-
tion program can execute another function. The latter,
however, cannot properly execute yet another function.
Program
LEVEL 1 LEVEL 2 LEVEL 3
Press
Resumes LEVEL 1
calling program
Does not resume
Stop actual LEVEL 2
calling program
Note that:
1. can prefix a digit as well as a top row key, thus
allowing up to 15 unique labels. We shall presently
use a digit label in a program that repeats.
2. can be used if pressed manually to move the pro-
gram pointer to the top of memory. We shall use this
to start execution at the very first step in program
memory.
3. If a program calls another programmed function, the
terminating the function does not cause a stop,
but rather resumes the sequential execution of the
calling program.
Figure 4-2. Control Operations for Defining Functions (cont.)