Radio Shack TRS-80 Model III - Page 46

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JI
TRS-80
MODEL
III
Printer
Control
Features
Output
to a printer
involves
several
variables:
• Maximum
line
width
(How many
print
columns
are there?)
•
Page length
(How many
print lines
are on
a page?)
• Printer
status
(Is
the printer
connected
and ready
to receive
data and
print
it?)
In
this
section
,
we will
explain how
to
set up
the Model
III to
control
all these
variables.
Setting
the
Maximum
Line
Length
In Model
III BASIC,
you can preset
the maximum
line length.
If
a
line
exceeds
the
preset
length,
the
Computer will
automatically
insert an
end of line
(carriage
return)
so that
the rest
of the line
will
be output
on a new line.
The following
paragraphs
explain
why
you may
want
to do this
.
One
important
difference
between
display
output
and printer
output is
the
maximum
line l
ength.
(A
"
line" is
a stream
of
data characters
terminated
by a
carriage
return
(
ENTER)
.
)
The Model
III Display
has
a
maximum
line
length
of 64 characters
. If you
PRINT
a
line longer
than this
,
the
Computer
simply
"
wraps
around
"
to the
beginning
of
the
next
line.
Printers
have
a maximum
line
length,
too, but this length
differs
for various
models.
The
response
to
an overflow
(longer
than
maximum-length)
line
also
varies.
Some
models
wrap
around
to
the next line
automatically.
Others may
lose
the extra
data,
and may
begin
abnormal
operation
when
the line
is too
long.
Another
consideration
is paper
width
. Suppose
your
paper is only
wide
enough
to
hold
80
characters
—
but the printer
will
accept
lines of
up
to 1 32
characters
. In
this
case,
if you
send
a line
longer
than
80 characters,
the printer
will
print
part
of the
information
past
the
edge of
the
paper.
How
to Set
the Line
Length
Memory
address
16427
contains
a value
equal
to the
maximum
line
length
less
two.
For
example,
to set
the
maximum
line
length
to
64,
execute
the
BASIC
statement:
POKE
16427,
62
Since
the
Display
is
64
characters
per line
(cpl), this
setting
will
make
line
printer
output match
Video
Display
output.
36