4/Technkal and
Programming
Information
The
Modem II accepts data from a computer,
converts that data into tones and then sends the
tones
over telephone lines to another modem. It also
accepts tones from telephone lines and
changes those tones
into data that your computer
understands.
The following criteria must be met before
computer-to-computer communication can take place.
©
Both computers
must have the same communication
protocol:
H
Baud Rate (0-300)
[X]
Word Length
Parity
[X]
Number
of
Stop
Bits
See
your Computer owner's manual to find out
how
to set
communication protocol.
•
One Modem must be in the ORIGinate Mode and the
other must
be
in the ANSwer
Mode.
Usually, if you call another computer, you should be in the ORIGinate Mode. If you
receive
a
call, you should be in the
ANSwer
Mode.
®
If you're using
a
Modem II with a TRS-80 Color Computer,
always
keep the FORCE DTR
Switch
(on the back
of
your
Modem) ON.
Space
Disconnect
Your Modem
will
drop the phone line any time it
receives
a continuous RS-232 SPACE (ASCII
BREAK or null with no start and stop bits) for three seconds from the remote modem or for 1
.5
seconds from your Computer. This
is
called "space disconnect" and is in accordance with
Bell
103J
standards
for short and long space
disconnect. In all modes except
TEST, your Modem will
disconnect itself from the phone lines if it
receives
a loss of carrier greater than 300 milliseconds.
To regain control
over
your Modem after it
receives
a Space Disconnect
while
in the MANual
Mode, switch to AUTOmatic Mode or turn the POWER Switch to OFF. Then reset
the Modem
switches as desired. If your Modem receives
a
Space Disconnect while
in the AUTOmatic Mode,
the Modem
will
execute the front panel switches.
When
you use your Modem II in AUTOmatic Mode, you don't have to
dial any numbers or pick
up
your telephone receiver
to
answer
a call
—
your Modem does all that for you.
As long as
you're going
to be at your Computer throughout communications, you can control
the Modem
—
and your telephone
—
through your
Computer keyboard. This is another easy way
to run certain
communications
programs such as
Videotex.
You can also send
or
receive
data from another computer while you're
not at your Computer
keyboard. Just
write
a BASIC or machine-language program
and use the commands
described in
this manual (See Appendix
B) to program your Modem to dial a number
or
answer
the phone
unattended.
By programming your Modem to download daily receipts
to another
computer at
15
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