Radio Shack TRS-80 Modem II - Page 23

Modem
II
Programming Mode
The Modem
II contains a custom
8-bit
microprocessor which
has user memory that
allows
the
Modem to
dial a number
which can be up to 25
digits in length.
The Modem may dial the
number
from either
AUTO/ORIGinate or
AUTO/ANSwer
Mode.
Before
programming the
Modem, you must put
it in
programming mode. You can do this
two
ways:
®
Setting FORCE
DTR to ON and
then sending an
asterisk
(*) to the Modem.
•
Setting FORCE
DTR
to
OFF and
then sending an
asterisk
(*) or disasserting (turning off)
DTR from the
Computer or Terminal.
When can you
program the
Modem
II?
When the
Modem is in
AUTOmatic Mode and
an "idle state,"
it can be
programmed.
An idle state is
defined as:
•
The Modem is
in AUTO Mode
and not in Test
Mode.
•
The Modem is
not connected to
the phone line
(OH Light is
off).
•
The Modem is
not in the process
of answering a
call.
•
DTR is asserted
(turned on) by the
Computer
or
by
the
FORCE DTR
Switch.
The
idle state occurs if the
appropriate
MODE
Switch is set to
AUTO when the
power
is
turned
on or after the Modem
has received a
disconnect (loss
of carrier
or SPACE)
while
in AUTO
Mode.
The
FORCE
DTR Switch
The
main purpose
for the FORCE
DTR Switch is
to
allow
the
Modem II to be used
with
the
TRS-80 Color
Computer. The
Color Computer
does not
have DTR (Data
Terminal Ready) as an
RS-232
control line. Also, some
other
terminals which use
a three-wire RS-232
scheme (ground,
data in, and
data out) could
not be used with
the Modem.
The Modem II uses
the DTR line as
its master
control line.
In all operation modes,
DTR must be
asserted to
cause the internal
microprocessor to
execute its
program.
Here are the rules for DTR:
•
The Modem
will not execute the
front panel
switch settings
until DTR is
on if DTR is off
during
power-up.
•
The
Modem will
immediately drop
carrier and
disconnect from
the phone line if DTR is
off
while the Modem is
on-line with
another modem.
After a three
second delay, the Modem
II
will
be
in
programming mode (if the
front
panel switches are
in AUTO Mode and
DTR is still
OFF) or go into a
"sit" mode if the
Modem is
in MANual
Mode.
•
The
Modem will
execute the front
panel
switches if DTR is
reasserted after the
Modem has
disconnected from the
phone lines.
17