Radio Shack TRS-80 Modem II Operation Manuals page 27

I
'
'
.
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I
After the
Modem
has
dialed the
number,
it
forces carrier detect for
two
seconds
—
then
releases
it.
This time period allows the receiver
filters
to stabilize
from
the
impedance change
presented
by
the
phone
line.
The
Modem
then waits
for carrier
from
the
remote
modem
for a period of 12
seconds.
If
carrier
is
detected, the
Modem
asserts carrier detect to
the
Computer.
If carrier
is
not
detected, the
Modem
drops
the
phone
line
and,
after a three
second delay, executes the front
panel switches.
The
Modem
override (from
AUTO/ANS
to
AUTO/ORIG)
is
programmed by
entering the
programming mode,
sending a
number
to
dial,
and executing
by
asserting
DTR.
The
Modem
will internally
switch
filter
banks and transmit/receive frequencies
under microprocessor
control.
It
will
then
act
exactly as
if
the
Modem
was
in
AUTO/ORIG
Mode.
After
a
disconnect,
it
will
go
back
to
AUTO/ANS
Mode. The
override
program
is still
intact as
long
as
power
is
applied. If
further
overrides are necessary, place the
Modem
in
programming
mode
and
either
re-program
the
phone
number
or
send an
X
and
assert
DTR.
See
Appendix
B
for a
complete explanation of
the
Modem
programming
codes.
AUTO/ANSwer
Operation
Another
unattended use of the
Modem
II is
in
an
AUTO/ANSwer
environment.
The
Modem
is
easy
to
use
in this
mode.
To
use
the
Modem
II
in
AUTO/ANSwer
Mode:
1
.
Set the
MODE
Switches
to:
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tM*a**m *>wru
POWER
2.
Assert
DTR
(by the
Computer
or
by
the
FORCE DTR
Switch).
3.
Set the
Modem's
POWER
Switch
to
ON.
The
ON
and
TR
Lights
will
go on.
After the
phone
rings, the
Modem
seizes the
line,
delays for
two
seconds,
and
transmits carrier.
It
then waits 12
seconds for the
remote
modem
to
send
carrier. If
it
does
not see the
remote
carrier,
it
disconnects
from
the
phone
line,
delays three
seconds,
and
goes
back
to
AUTO/ANSwer Mode
and waits for the next
call.
There
may
be
some
instances
when
it
is
desirable to
tell
the
Modem
not
to
answer an incoming
call
or
to
hang up on a
call in
progress.
This
is
done by
either
turning
FORCE DTR
OFF
or
by
placing the
Modem
in
the
LOCal
Test
Mode.
This
is
only
practical if
FORCE DTR
is
off since
the
only
way
to get out
of
a
LOCal
Test
(programmed by
the
Q command)
is
to set
the
Modem's
FORCE DTR
to
OFF. The
LOCal
Test resets the ring detect circuitry
inside the
Modem
so
incoming rings are
ignored.
21