Expanding Program Memory; The 000 Instruction And Program Line 000 - HP 12C Platinum Owner's Handbook Manual

Program line 007 contains the last instruction you keyed into program memory.
However, if you press Ê again, you'll see that this is not the last line stored in
program memory:
Keystrokes Display
Ê 008,43,33,000 Program line 008
As you should now be able to tell from the keycodes displayed, the instruction in
program line 008 is gi000.
The 000 Instruction and Program Line 000
i
Whenever you run the program now stored in program memory, the calculator
executes the instruction in line 008 after executing the seven instructions you
keyed in. This i000 instruction – as its name implies – tells the calculator to
"go to" program line 000 and execute the instruction in that line. Although line
000 does not contain a regular instruction, it does contain a "hidden" instruction
that tells the calculator to halt program execution. Thus, after each time the
program is run, the calculator automatically goes to program line 000 and halts,
ready for you to key in new data and run the program again. (The calculator is
also automatically set to program line 000 when you press fs to set the
calculator from Program mode to Run mode.)
The i000 instruction was already stored in line 008 – in fact, in all program
lines – before you keyed in the program. If no instructions have been keyed into
program memory, if Continuous Memory is reset, or if fCLEARÎ is
pressed (in Program mode), the instruction i000 is automatically stored in
program lines 001 through 008. As you key each instruction into program
memory, it replaces the i000 instruction in that program line.
If your program should consist of exactly eight instructions, there would be no
i000 instructions remaining at the end of program memory. Nevertheless,
after such a program is executed the calculator automatically returns to program
line 000 and halts, just as if there were a i000 instruction following the
program.
If you key in more than eight instructions, program memory automatically
expands to accommodate the additional instructions.

Expanding Program Memory

If no instructions have been keyed into program memory, if Continuous Memory
has been reset, or if fCLEARÎ has been pressed (in Program mode),
Section 8: Programming Basics 91