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140
Simple Programming
Labels and Step 000
The labels (3 through &, £ (3 through [ (&, (@ through (3)) in
your programs act as addresses—they tell the calculator where to
begin or resume execution. When a labelis encountered as part of a
program, execution merely ''falls through'' the label and continues
onward. For example, in the program segment shown below, when
you pressed [, execution would begin at (50 £¥ and continue down-
ward through program memory, on through the
(3) instruction,
and continue until the
was encountered and execution was
stopped.
When you press ¥ ...
o
o
...execution begins here.
No
here...
0
B
so execution falls through
the
instruction...
/_\
...and continues to the [RTN].
Execution falls through step 000, too. You can load instructions into
steps 001 through 224 of program memory, but you cannot load an
instruction into step 000. In fact, step 000 merely acts as a kind of
label in program memory, a beginning point for the loading of a
program. When step 000 is encountered by a running program, execu-
tion continues without a halt from step 224 to step 001, just as if step
000 were not there.
Flowcharts
At this point, we digress for a moment from our discussion of the
calculatoritself to familiarize ourselves with a fundamental and ex-
tremely useful tool in programming—the flowchart.
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