Installation guide

5-17

Using Ethernet Modem

Dial-in

NPort Express listens for a TCP/IP connection request from the remote Ethernet

modem or host. NPort Express’s response depends on the ATS0 value, as

outlined below.

ATS0=0 (default):

NPort Express will temporarily accept the TCP connection and then send the “RING”

signal out through the serial port. The serial controller must reply with “ATA” within

2.5 seconds to accept the connection request, after which NPort Express enters data

mode. If no “ATA” command is received, NPort Express will disconnect after sending

three “RING” signals.

ATS0

≧

NPort Express will accept the TCP connection immediately and then send the

“CONNECT <baud>” command to the serial port, in which <baud> represents the

baud rate of NPort Express’s serial port. After that, NPort Express immediately enters

data mode.

Dial-out

NPort Express accepts the AT command “ATD <IP>:<TCP port>” from the

serial port and then requests a TCP connection from the remote Ethernet Modem

or PC. This is where <IP> is the IP address of the remote Ethernet modem or PC,

and <TCP port> is the TCP port number of the remote Ethernet modem or PC.

Once the remote unit accepts this TCP connection, NPort Express will send out

the “CONNECT <baud>” signal via the serial port and then enter data mode.

Disconnection request from local site

When NPort Express is in data mode, the user can drive the DTR signal to OFF,

or send “+++” from the local serial port to NPort Express. NPort Express will

enter command mode and return “NO CARRIER” via the serial port, and then

input “ATH” to shut down the TCP connection after 1 second.

NOTE The “+++” command cannot be divided. The “+” character can be

changed in register S2, and the guard time, which prefixes and suffixes

the “+++” in order to protect the raw data, can be changed in