Radio Shack TRS-80 Model III - Page 53

Programming
the
RS-232-C
Interface
In
this section,
we
will treat the
RS-232-C
just like
any
other
input/output
device,
and
will explain
how your
BASIC
program can
use
it. In
Technical
Information,
we
explain how to
use it in
a
machine-language
("Z-80")
program.
For
details about
the RS-232-C
signal
conventions
and
theory of
operation, see
the
Appendix.
Selecting
the
RS-232-C
Characteristics
Before
using the RS-232-C
interface to
communicate
with
another
device, you must
be
sure
your RS-232-C
is set up to
match
the
requirements
of the
other device
.
So start by
getting the
following
information
about
the
other device.
In
the right
column, we
list typical
values used.
Characteristic
Typical
Values
Used
BaudRate
110,150,300,600,1200,
2400,4800,9600
Word
Length
(bits)
5,6,7,8
Parity
Even, Odd,
None
Stop
Bits
1
,
2
When you
start
the
Computer,
the
RS-232-C
is
initialized to
the
following
"default
characteristics":
BaudRate
300
Word
Length
(bits)
7
Parity
Even
Stop
Bits
1
In addition,
the
RS-232-C
is
initialized to
wait for
completion
of character
I/O
before
returning.
That
is, if you
attempt
to
receive a
character,
the
Computer
will wait
until
a
character
is
received;
it
will never
return to
you
without a
character.
Similarly,
if you
attempt to
send a
character,
the Computer
will
wait until
the
receiving
device
is able to
accept
the
character.
OPERATION
To
regain
control
of the
Computer
during a
wait,
hold
(BREAK)
until READY
returns.
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