Moxa Technologies NPort Express User Manual

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Introduction

NPort Express’s new Ethernet Modem operation mode is designed to provide true modem emulation, in
which NPort Express emulates a regular serial modem, accepting AT commands for dial-in/out service
and then transparently passing raw data in/out after the user initiates the Ethernet Modem mode.

After a connection is established, NPort Express acts as a gateway between the serial line and Ethernet
LAN, making it possible for raw RS-232/422/485 data to travel across a local LAN. After receiving raw
serial data, NPort Express will prefix and postfix a TCP/IP header and trailer, and then send it out to the
Ethernet medium. Once the control host receives the TCP/IP data frame, the NOS (Network Operating
System) recovers the raw data by decoding the TCP/IP header and trailer. The user can easily capture the
raw serial data from the Ethernet medium using Telnet or some customized TCP/IP socket program,
providing an ideal long-distance serial data transmission solution between host and serial device.

Application Architecture

Two typical applications:

(1)

(2)

. Note: If the DCD signal for carrier detection is required, you will need to use a cable to connect

NPort Express’s serial port to your device/PC, as shown here:

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NPort Express Configuration

. Note: This function is available in firmware version 1.01.81 or above for NPort Express

1. Enter NPort Express’s configuration screen using either Telnet over a LAN, or Moxa PComm
Terminal Emulator via NPort Express’s RS-232 Console port.

2. Open the “serverConfig” screen, and then change the “Operating Mode” to [Ethernet Modem].

3. Open the “Serialport” screen and set “TCP port no.” and “Destination IP”.
NOTES: 1. “TCP port no.” has default value = 4001

2. Only the device with IP set to “Destination IP” will be allowed access or leave empty for

all devices

4. Restart NPort Express’s operating system.

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>=1: 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 box 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 side]

When NPort Express is in data mode, the user can drive DTR signal to OFF or send the “+++” from local
serial port to NPort Express. NPort Express will enter the command mode and return the “NO
CARRIER” via serial port, and then input “ATH” for shot down tcp connection after 1 second.