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44 Chapter 7 Special Features: Modem Emulation
connects to the IP Address of the server when an
ATDT ipaddress:port (ATDT 192.168.25.5:50001)
command is issued. Once the remote device establishes the TCP
connection, a CONNECT message is sent to the serial port and only then
does the Digi device switch from AT command mode to data mode. Using
the modem escape sequence or dropping DTR on either side terminates
the connection. A DISCONNECT message will be sent to the application if
the remote side closes the TCP connection.
In Diagram B, two Digi devices will replace modems on both sides of the
connection. The initiation of the connection occurs with either of the Digi
devices. If both ends are Digi devices, the TCP listening port number is
50001 for port 1. An example of the connection command is ATDT
192.168.25.30:50001. Upon establishing a successful TCP
connection, a CONNECT message is sent to the serial port and only then
does the Digi device server switch from AT command mode to data mode.
After the CONNECT is received, the transmission of data begins. Using
the modem escape sequence or dropping DTR on either side terminates
the connection.
Modem emulation has the ability to communicate to an infinite number of
other devices.
Modem Emulation Cable Signals
Use the following signal assignments to make a cable connecting the Digi
device to a serial device.
D
I
G
I
O
N
E
T
S
D
I
G
I
O
N
E
T
S
192.168.25.30
Workstation
Digi One TS
#1
Digi One TS
#2
Ethernet
Serial cable
User Scenario-Diagr am B
Serial cable
Workstation
Serial Device Digi Device
CTS (in) RTS (out)
RTS (out) CTS (in)
DSR (in) DSR (in)
DTR (out)