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IBM 1620 - Writing the 1620 FORTRAN Program

IBM 1620
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cessively
higher
pairs
of
memory
locations.
Each
2-digit
memory
character
is
decoded
into
the
proper
numerical,
alphabetic,
or
special
character
by
the
output
translator
and
presented
to
the
plotter.
The
P-address
of
the
instruction
must
designate
the
odd
-numbered
memory
location
at
which
the
numerical
digit
of
the
first
character
to
be
transmitted
is
stored.
The
zone
digit
of
the
first
character
is
located
at
the
next
lower
memory
address
(P
minus
1)
which
is
an
even
address.
Increment
plus
2
is
used
to
provide
memory
addresses
for
successive
character
s.
If
an
even-numbered
memory
location
is
erron-
eously
designated
by
the
P-address,
data
presented
to
the
plotter
is
incorrect
and
parity
errors
may
occur.
Output
data
may
consist
of
a
random
mixture
of
numerical
and
alphabetic
characters
which
exist
in
memory
as
two-digit
characters.
If
an
attempt
is
made
to
write
a
record
containing
single-digit
num-
erical
characters
by
means
of
this
instruction,
invalid
combinations
of
disassociated
numerical
digits
are
the
result
and
parity
errors
may
occur.
Flag
bits
existing
in
memory
locations
from
which
an
output
record
is
written
are
not
transmitted
to
the
plotter.
The
write
operation
leaves
output
data
unchanged
in
memory.
227-5811-0 (11-63)
Transmission
of
a
character
of
output
data
to
the
plotter
requires
plotter
motion
corresponding
to
the
paper
tape
code
for
the
specific
character.
A
space
is
ignored
by
the
plotter.
The
Write
Check
latch
is
turned
on
when
the
following
condition
exists:
A
character
with
incorrect
parity
is
pre-
sented
to
the
plotter
by
the
output
trans-
lator.
If
the
Write
Check
latch
is
turned
on
with
the
plotter
as
the
output
device,
the
plotter
is
stopped
after
the
corresponding
plotter
motion
is
complete.
With
the
plotter
as
the
output
device,
the
write
operation
is
terminated
by
one
of
the
following:
1.
Sensing
a
record
mark
at
an
odd
memory
address.
Termination
of
the
write
opera-
tion
directs
the
computer
to
enter
the
I-cycle
for
the
next
instruction
in
sequence.
2.
Pressing
the
Release
key
on
the
console.
The
write
operation
is
terminated
immedi-
ately
and
the
computer
stops.
Pressing
the
Start
key
on
the
console
is
required
to
restart
the
computer.
Circuit
Objectives
See
Write
Numerically
(Code 38).
2.3

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