The 000 Instruction And Program Line 000; Expanding Program Memory - HP 12C Platinum User Manual

114 Section 8: Programming Basics
The 000 Instruction and Program Line 000
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 or when fCLEARÎ is pressed in 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), program
memory consists of 8 program lines, and there are 20 storage registers available
for storage of data.