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Solving
the Critical Problems fo Serial Device Communications through
Dual LAN Connections and Multi-Access Functionality
In serial
communications, speed and convenience are the two most important
points. For real-world applications, there are numerous serial
devices in the industrial environment that need to connect
to various hosts for control. Early systems used dedicated
copper lines to connect these serial devices and vendor-specific
proprietary serial protocols for industrial applications.
While adequate for many applications, a one-cable, one-device
system presents issues of limited transmission distance, limited
hardware resources and limited interface options of each serial
device.
Recently,
the advent of Ethernet has made it possible to solve the distance
and interface limitations of serial devices. Ethernet is a
ubiquitous solution that has established itself as the principal
industrial network through a combination of high data rate
and shelf infrastructure.
Based
on the trend of Ethernet, serial device servers are designed
to network-enable any device using the RS-232 or RS-422/485
serial communication protocol. By encapsulating serial data
and transporting it over Ethernet, the serial device servers
allow virtual serial links over Ethernet and IP (TCP/IP, UDP/IP)
networks. After COM redirection software installation, standard
serial operation calls are transparently redirected to the
serial device servers, guaranteeing compatibility with legacy
serial devices and enabling backwards compatibility with existing
software. As a result, you can extend the distance of the
serial connections within the plant, throughout the factory,
the facility, the office building, or across a global enterprise.
The ARC
report estimates that by 2011 the market opportunities for
industrial Ethernet will exceed US $900 Million. This means
that almost any communication device in the world can be part
of this booming market, if it has the right interface. The
interface of the serial devices should be transformed to keep
up with Ethernet trends.
To take
advantage of this tremendous market opportunity, industrial
devices need to be developed more customer-oriented. Additionally,
the immediate benefits of Ethernet-enabled serial device servers
include:
- Efficient
Communications - Instead of having one device communicating
with one computer, one device can communicate with every
computer on a network.
- Lower
Cost of Ownership - Some serial devices already have the
proper interface for Ethernet communications. There is no
need to upgrade an existing serial device to newer, costlier
version just to have a built-in Ethernet interface.
- Extended
Life of Software - Many existing software can be used to
communicate with the serial device as if connected to a
local COM port.
Although
serial device servers offer an easier way to network RS-232,
RS-422/485 serial devices, there are still some limitations
about current serial device servers. Using a serial device
server, the device can communicate to only one computer on
network in a set period of time. The data from the device
is transferred to this computer only. No others can share
this data. Most serial device servers provide only one LAN
port. If this connection fails, the device can not connect
to the host anymore. Some serial device servers provide two
LAN ports and only support the cascading connection (Daisy
Chain). It's better than the only one LAN port module, but
if one of the connections fails, the modules behind this path
will lose connection.
Considering
the pros and cons of serial device connections and the rising
advent of Ethernet, Advantech's EKI RS-232/422/485 serial
device servers combine rugged, compact and fast 1 or 2 RS-232/422/485
serial ports with 2 LAN ports and 2 power inputs for redundant
networking. With this advanced technology, EKI serial device
servers have two powerful features to ensure transmission
stability; "Simultaneous Dual-LAN Redundancy", and
"Advanced Multi-Access Functionality".
Simultaneous
Dual-LAN Redundancy
With redundant LAN connections, communication is not interrupted
in the event of a network problem. With one connection automatically
assigned as the primary and the other as a backup, the loss
of the primary connection initiates an immediate and automatic
switch-over, ensuring data integrity and peace of mind.
Advanced
Multi-Access Functionality
Instead of the unique one cable-one device system required
by RS-485 Modbus systems, Ethernet permits the use of servers
and gateways through which serial data is transported over
an Ethernet network to the recipient host. Advantech provides
powerful Serial-to-Ethernet, Ethernet-to-Serial serial device
servers. EKI Serial Device Servers combine various operations;
such as COM port redirection, TCP server/client and UDP mode
to fulfill advanced needs.
EKI-1000
series also supports Multi-Access functionality to provide
5 host connections for each serial port with broadcast and
polling operations. In broadcast mode, EKI Serial Device Servers
handle a command from one application and reply to the data
from the serial port to all applications connected to this
serial port. In polling mode EKI Serial Device Servers handle
the commands from one application and reply to this application
only. Query from other applications must be queued and wait
for current process completion.
Below
is a list of a few key Advantech Serial Device Servers:
Through
Dual-LAN redundant connections, EKI Serial Device Servers
greatly improve connectivity, reliability, system stability,
and simplify redundant configurations, regardless of whether
the devices are in the same domain or not. And by using Serial
Device Servers to share serial devices, users can eliminate
separate serial lines and serial devices attached to individual
hosts. Collecting the data from these serial devices is easier
and more effective.
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