User guide

Modem Mode
In Modem (Emulation) Mode, the unit presents a modem interface to the attached serial
device. It accepts AT-style modem commands, and handles the modem signals correctly.
Normally, there is a modem connected to a local PC and a modem connected to a remote
machine. A user must dial from the local PC to the remote machine, accumulating phone
charges for each connection. Modem Mode allows you to replace modems with NetPorts, and
to use an Ethernet connection instead of a phone call. By not having to change
communications applications, you avoid potentially expensive phone calls.
To select Modem Mode, set the Connect Mode to C6 (no echo), D6 (echo with full verbose),
or D7 (echo with 1-character response).
Note: If the unit is in Modem Mode, and the serial port is idle, the unit can still accept network
TCP connections to the serial port if Connect Mode is set to C6 (no echo), D6 (echo with full
verbose), or D7 (echo with 1-character response).
Modem Mode Messages
• Received commands must begin with the two-character sequence AT and be
terminated with a carriage return character.
• The unit ignores any character sequence received not starting with AT, and only
recognizes and processes single AT-style commands. The unit treats compound AT
commands as unrecognized commands.
• If the Full Verbose option is in effect, the unit responds to an unrecognized command
string that is otherwise formatted correctly (begins with AT and ends with carriage
return) with the OK message and takes no further action.
• If the 1-Character Response option is in effect, the unit responds to an unrecognized
command string that is otherwise formatted correctly with ‘1’ and takes no further
action.
• When an active connection is in effect, the unit transfers data and does not process
commands received from the serial interface.
• When a connection is terminated or lost, the unit reverts to command mode.
• When an active connection is in effect, the unit terminates the connection if it
receives the following sequence from the attached serial device:
o No serial data is received for one second.
o The character sequence +++ is received, with no more than one second
between each two characters.
o No serial data is received for one second after the last + character. At this
time, the unit responds affirmatively per the selected echo/response mode.
o The character string ATH is received terminated with a carriage return. The
unit responds affirmatively according to the selected echo/response mode
and drops the network connection. The serial interface reverts to accepting
command strings.
• If this sequence is not followed, the unit remains in data transfer mode.
Modem Mode Commands