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Virtual serial port communication over Ethernet.

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VIRTUAL SERIAL PORT TECHNOLOGY BASICS

What is it ? , Exchanges of data with a remote serial port, Exchanges of data with a remote serial port, Virtual serial port client, Virtual serial port server, Devices with virtual serial port server, Virtual serial port client driver.

A Software Driver To Emulate And To Redirect Serial Port

A "virtual serial port" is a software function (a driver indeed) emulating a hardware serial port, and used to exchange data in the respect of some serial communication protocol, in order to redirect these data towards a terminal using another data transmission technology.

According to the automation field, this functionality can be useful when the virtual serial port redirect the data through an Ethernet port.


A virtual serial port can be used as a communication interface when :

Exchanging Data With A Remote Serial Connection Over Ethernet
Diagnostic software running into a PC with a RS 232 HART modem to interface locally an Optiflex 1300c HART sensor.

To illustrate this, let's take as an example a software used to diagnose a measurement device, which can connect by using a RS232 line only in order to access data into a "time domain reflectometry" (TDR) radar level sensor, such as the "Optiflex 1300C" HART sensor from the "Krohne" company (what imposes to install a HART modem as communication interface with the sensor).

Maintenance PC in Sweden communicating with HART sensor in New Zeland with RS 232 remote connection and with virtual serial port over Ethernet.

Let's take as an hypothesis you are operating at a client's office in Sweden (Hallå, hallå !), and that you wish to establish the diagnostic of a remote sensor located on a site of our friends Maori (Kia ora, kia ora !) in New Zeland, near Auckland.

It is not reasonable to want to interconnect the devices by installing a RS 232 line or an USB line of about 20 000 kms length.


Virtual serial port client and virtual serial port server over IP between a diagnostic software and a remote sensor, with HART modem, level sensor and ADSL modem.

One available solution can be using the services of virtual serial ports, which are installed :

Each station contains an ADSL modem, a GPRS modem, a satellite communication modem or any other Ethernet compliant modem. The data will be transmitted over an Ethernet network, and in this case probably via Internet.

One of the benefits the usage of virtual serial port over Ethernet affords is that since the communication is entirely digital, it is very stable and very robust according to the electromagnetic perturbations.

Virtual Serial Port CLIENT Over IP
Virtual serial port client over Ethernet.

This virtual port is client according to the data, that is it will initiate requests and it will send commands.

(Reading requests, writing requests, command requests etc)

Configuration

Operating description

Virtual Serial Port SERVER Over IP
Virtual serial port server over Ethernet connected to a HART modem and to a HART sensor.

This virtual serial port is server according to the data, that is it will serve the data answering the requests initiated by the client.

Configuration.

Operating description

Devices Providing Virtual Serial Port SERVER Services
ADSL modem or Ethernet switch including a virtual serial port server connected to a RS232 port.

Whether none automation application is required (no more than any other programmed application), a cheaper solution to install a "virtual serial port server" is to get an Ethernet switch, an Ethernet router or an Ethernet compliant modem (ADSL, satellite etc) providing this service and including a hardware serial port (RS 232 or USB for instance).

In this case, the device drives the data from the external Ethernet port towards the internal Ethernet port Nr 'm' (the Ethernet interface of the virtual serial port) when the Ethernet port Nr 'm' is the required destination, and it drives the data out through a local port whether the required address is not the 'm' port.

Reciprocally, when the virtual serial port receives data on its serial interface, it drives the data through the Ethernet 'm' port, and then to the external Ethernet port.


About the commercial programmable controllers, the eWon PLC provide the virtual serial port server capabilities in association with hardware RS232 port, for instance.


About the open source programmable controllers operating under Linux like "Proview", or any other device using this OS, it is enough to operate a only software solution by using the different tools provided by the operating system.

With Linux, different techniques can be used to implement a virtual serial port server : by using various flow redirecting commands, terminal configuration commands, piped commands, or / and programming in 'C' language, according to what is needed.

Virtual Serial Port CLIENT Drivers And Software

You will find many virtual serial port client software on the Web. Below is a list of some free drivers operating well.


For MS windows OS :


For LINUX OS :

Concerning controllers operating under this system, installing a virtual serial port client is like installing a server (see above) : using the Linux commands and programming.

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