NOTE:
Please
not
that device assignments changed
by
this address may not be reflected
in
CONFIG main menu 5.
Do
not set the same value
as
the code.
5.7.6 Bios Subroutine for the Speaker
om
Entry
Point: WBOOT + 36H
BEEP
is
the
entry point for the subroutine which sounds the speaker.
Entry
parameters
Register C 0
C = 1
to
FF
turns the speaker off.
The speaker sounds
for
an
interval
of
[C] x 0.1
secs
Register
DE
sets
the
frequency
of
the
sound
according to the expression:
(DE) =
10
6
3.2 x Frequency (Hz)
5.7.7 BIOS Subroutin.es for the RS232 Port
The following routines can be used
to
operate
the
RS-232C interface. Details
of
the RS-232C interface are given
in
Chapter
4.
The interface supports all commonly used transmission rates,
up
to
19,200 bps.
In
general it
is
not
possible
to
transmit
and
receive
at
different rates. Since some
databases (e.g. the
European
Videotext databases) use
75
bps transmit
and
1200 bps receive this option
is
available together with the reverse 1200 bps trans-
mit/75
bps receive. '
The interface is initialized using the RSIOX routine,
but
can also be initialized
by
BASIC
and
partially by
the
CONFIG
program. The operating system uses
a
261
byte buffer. Characters overflowing this buffer are lost. The size
of
the
buffer
can
be
increased by the RSIOX routine.
The interface should
be
opened before attempting
to
send
data.
The
interface also supports
XON/XOFF
and
SIISO
in
communication. These
are described
in
Chapter
4.
5-20
The
SI/SO
function only applies in 7 bit transmission.
When
SIISO
= 1,
no
action is taken.
When
SI/SO
= 0,
if
a SI character (OFH) is received, subsequent characters
will have a
"0"
added as
the
MSB
to
complete the byte. When
SIISO
= 0,
if
a SO character (OEH) is received, subsequent characters
in
the
range 20H
to
7EH
will have a
"1"
added as the MSB
to
complete
the
byte. Characters
OOH
to
IFH
and
character
7FH
will remain unchanged.
The
XON/XOFF
protocol allows the receiving device
to
tell
the
sender
to
wait
while it catches
up
on
processing.
When
XON/XOFF
= 1
no
action is taken.
When
XON/XOFF
= 0 a transmission
off
character CTRL-S (13H)
is
sent when
the
buffer
becomes more
than
three-quarters full, so
that
processing can catch
up. A transmission
on
character CTRL-Q (OIIH)
is
sent when
the
buffer
be-
comes less
than
one-quarter full, so
that
transmission can begin again. This
makes it possible
to
prevent the
buffer
overflowing
and
the loss
of
characters.
Entry
Point:
WBOOT
+ 39H
RSOPEN
is
the entry
point
for
the
subroutine which initializes the RS232C in-
terface for communication according
to
the
conditions set with
the
CONFIG
program. This subroutine turns
on
the power supply
to
the
RS-232C interface
(and
the
serial interface)
and
performs processing
to
prevent noise from being
output
over
the
line.
When
this routine is called, the former RS-232C condi-
tions are reset; therefore, any
data
remaining
in
the receive
buffer
at
the time
of
the
call
is
lost.
Entry
Point: WBOOT +
3CH
RSCLOSE
is
the entry point for the subroutine which disables communication
through
the RS232C interface.
Entry
Point: WBOOT +
3FH
5-21
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