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6
•
OGRAMMI
HE 91008
INTRODUCTION TO PROGRAMMING
NES
The 91008 has subroutine
capability.
A subroutine is a
se-
quen ce of program steps which is to be used many times, but
which is stored only once in the
memory.
The program may
'call for
' (i.e.
branch to) the subroutine at any point designated
in the
program.
When the subroutine is completed the program
automatically returns to the step following the program step
from which the subroutine was 'called
'.
Thus a repetitive sub-
routine may be stored only once in the memory yet used many
times throughout a program
;
this results in considerable sav-
ing of program memory
space.
Subroutines are fully described,
starting on Page
94.
The d isplay is blanked while a program is being run; when the
program
stops,
the calculator returns to the 'display mode'.
Many programs are short enough that the display will do no
more than blink before reappearing; a long program
,
such as
the diagnostic program, may leave the screen blanked for sever-
al seconds or even langer. lt is possible to write programs which
put the'calculator tnto a loop (it conttnually branches in a circle
and will never return to the display mode unless instructed to
do so)
;
when this occurs the keyboard is 'locked out' and no
key will work until the program is stopped, by pressing the
STOP key.
An error written into a program may result in an incorrect an-
swer or it may put the calculator into a loop so that it remains
blanked. When this occurs
,
press the STOP key and the dtsplay
wi II retu rn.
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