Tandy DCM212 Operation Manual page 32

Tandy
protocol
mode
operation
Serial
data going
to the
DCM
212
over the
RS-232C
cable
is
normally
in
a
marking
state.
When
you
press
a
key,
a
start bit
is
transmitted
(the serial line
goes
spacing)
for
a time depending
on
the speed of
oper-
ation.
The
bits
which
make
up
the
word
are
then
serially
shipped
to
the
Modem,
one-by-one.
These
bits
are
marking
or spacing
levels,
de-
pending
on
the type of
bit
(1
or
0).
The
last bit
to
be
transmitted
is
the stop
bit
and
it is
always a
marking
level.
When
the
DCM
212
receives
a
long space
from
the host
computer which
last 1.5
seconds or
longer,
it
will
go
into the
OFF-LINE mode
and
dis-
connect
from
the telephone
line.
The
long space
is
an
old
method
that teletype
machines used
to
say:
"Pay
attention
to
me!!!"
Several
lon g spaces
can
be strung together
by
multiple closures of a key
(usually
(BREAK)
).
This
string
of
spaces
can
tell
a
modern-day
modem:
"I'm
alt
done.
Go
ahead
and
turn
off"
The
long space
method
of disconnecting
a
modem
from
the
lines
is
known
as
a long space disconnect sequence.
Remember, you
can
turn
this feature
OFF
with the
/
command
parameters.
Condition 4
—
transmission of
the
abort
character
The
abort
character disconnect feature enables
you
to
disconnect
an
ON-LINE
DCM
212 without having
to
remember
about
long spaces
or shouting
into the telephone.
The
abort character can be used
in the
following
manner:
If
you
transmit the abort character
and do
not
transmit
any
other character
for 3 seconds afterward, the
Modem
will dis-
connect
from
the telephone
lines.
The
abort
character
can be
turned
OFF
by
typing
any key within
that
3-second
period.
The
/
command
parameters
are
set
up
to
allow you
to disable the abort character disconnect
feature.
The
abort character
(when
sent) uses
long space disconnect
signaling
to
tell
the other
end of
the
line
that
your
Modem
is
about
to shut
down.
This long space
signaling
is
only
true
if
you
have not
disabled
trans-
mission of
the
long space with
the
/
command
parameters.
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