Merging Ethernet and Serial Technology
Emerging Ethernet technology is providing
new ways of connecting legacy serial devices to a Local Area
Network (LAN) or Wide Area Network (WAN). It does not matter
what type of serial interface- RS-232, 422 or 485- the devices
in the applications are using; Ethernet Serial Servers allow
all three interfaces access to a LAN.
Ethernet Serial Servers connect a single
serial device or many serial devices to one LAN connection.
Ethernet Serial Servers are engineered to accept serial data,
convert it to Ethernet packets, transmit that information
onto the LAN and reconvert it to serial at the other end.
The most common Ethernet servers have 1, 2, 4, 8 or 16 serial
Communications with the connected serial
devices can be handled without changing existing serial programs.
The older legacy DOS programs that communicate via Com ports
1, 2, 3, or 4 on a computer can also be used in Ethernet applications.
The Ethernet servers can accommodate this by using Virtual
Com port software or a feature called Serial Tunneling (sometimes
called Nailed Down) configuration.
Serial Tunneling or Nailed Down configuration
can be set up in the Ethernet serial server using a built-in
configuration menu. Serial Tunneling basically means that
two Ethernet Serial Servers are used to make two different
serial to LAN connections. This can be on the same or different
subnets on the LAN.
Let's use a computer and a Serial Data
Acquisition device in this example. One Ethernet server will
be connected to the serial port of the computer running the
program. The second Ethernet server will be connected to the
serial connection on the Data Acquisition device. When each
Ethernet Serial Server has a LAN connection and power is applied,
communication between the two dedicated Ethernet servers automatically
start a session.
Simply put, once the two Ethernet devices
are used in the Serial tunneling mode they automatically transfer
serial data across the LAN as if it was transparent. The program
only opens the Com port and sends data out.
Remember when I said that the LAN is
transparent to the serially connected devices? That feature
opens the door to countless applications. Computers or similar
intelligent devices are not necessary to setup communication
between two serial devices using Ethernet Serial Servers and
the Serial Tunneling feature.
For example, let's say a scale needs
to send data to a display or a positioning camera needs to
send information to a controller on a manufacturing line.
The fact that the Serial Tunneling feature makes the LAN transparent,
the mentioned applications are feasible. Data received by
one Ethernet serial port will be transmitted out the other.
A second way of communicating to Ethernet
Serial Servers is with the use of Virtual COM Port software
on a Computer. When using this type of software only one Ethernet
Serial Server is needed to make the connection at the serial
device. The computer is connected using the Network Interface
Card (NIC). This type of software loads in the operating system
on the computer as another Com port.
Running a Windows operating system it
can be found in the device manager under Com ports. Each Com
port is linked with an IP address to a specific Ethernet Serial
Server. Once again the LAN is transparent to the software
program running the application on the computer. This type
of Virtual Com port can be used with most Windows programs.
However, DOS programs will not be able to open the virtual
I will talk in depth on serial tunneling
in the next issue of our E-connections. If you have questions
related to this article please feel free to drop me an E-mail.