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Section
5
Subroutines
Onen.
a
prog
ram
contai ns a ce
n ain seri
es
of
instruction
s that are
executed
sevenll time
s
throughout
the
progra m.
When the
same
set
of
instruct ions occ urs more
than once in
a program,
it
can
be executed as
a subro utine
.
A su brout ine is se
lected
by
the
IGsel
(go
to
slIbroutine)
operation. followed by
a
line
address
(0
1
thro
ugh
49).
A
tGSaI
instruction
transfers
execu
tion
to the routine
specified by the
line
address, just
like a
tGTol in
struction.
Howe
ver,
after
a
IGssl
in
st
ruction
has
been
executed and
the
running
program
executes a
I
FlTH
I
(
refilm
),
execution
is
then tran sferred
back
to the
nex
t
instruction
aft
er
the
IGSBI
.
Execution then
continues seq
uentiall
y
downward
thro
ugh
program memory
.
The illustra tion below shou
ld
make
the
distinction
between
IGTol and IGssl
more clear.
Branch
Line
00
t
IGTOI09
Line
09
----------~
[An~1
1"",1
Execution
stops here.
Subroutine
Line
00
Line
09
I
+
IGse l09
I
+
I
ATH
I
I
ATH
I
Execution stops
here.
60
J
~
~
~
~
~
E=
E=
e;::
e;::
E=
e=
e=
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