Radio Shack TRS-80 Model III - Page 55

OPERATION
If the Computer
is using the Don't
Wait procedure,
then
control will return to BASIC
even if no
character was received .
If the Computer
is using
the Wait procedure
,
control
will return to BASIC after
a
character is
received. Press (BREAK
)
to interrupt
a
WAIT and
regain keyboard control of
the Computer.
4. To make this
character available to
BASIC, execute a
BASIC statement
like:
A$
=
CHR$(PEEK(16872))
which stores the
string value in A$.
Remember, if A$
=
CHR$(0), then
no
character was received.
5
.
Repeat
Steps
3
and 4 until you
are through
receiving data.
To Change the
RS-232-C
Characteristics
If the TRS-80's
default characteristics
do not match
the requirements
of the other
device, you
can change some or all of
them
by
using
('
'calling") an
initialization
subroutine
that is stored in ROM.
Before calling SRSINIT,
you must store
the desired
characteristics in
certain RAM
locations:
Address
Contents
16888
Transmit/Receive
Baud Rate Code
16889
Parity/Word
Length/Stop Bit Code
16890
Wait/Don't-
Wait
Switch
Transmit/Receive
Baud Rate Code
The TRS-80 RS-232-C
allows you to
receive and transmit at
different rates. For
most
applications, the
rates will need to be
the same.
Instead
of storing the actual
baud rate
,
you
store
a
code
for the value
,
taken from
the
table
below. You select
the appropriate codes
for send
and receive rates,
and then
"pack'
'
them into memory
address 16888 as
follows:
Send/Receive Code
=
(Send
Code
*
16)
+
Receive
Code
For
example,
suppose
we want to
send
and
receive at 1
10
baud.
Using the table on
the next
page,
we find
that the code
for 1 10
baud
is
2.
So:
Send/
Receive Code
=
(2*
16)
+
2
=
34
45