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Interfacing RS232 instruments to a TCP/IP network
Most modern electronic instruments including bar code scanners,
measuring tools and laboratory instruments (balances, electrochemistry
meters, spectrometers, spectrophotometers, measuring instruments,
etc.) are designed to interface to a computer using a standard RS232
serial cable connection. The RS232 serial communications protocol
has been around for many years and is extremely well established
with a number of inexpensive hardware and software solutions available
for it. Almost all computers are equipped with at least one RS232
serial port with add-on serial adapters being widely available. There
are also hundreds of software applications available for communicating
with instruments through RS232 connections. Because of the flexibility
and the ubiquity of the RS232 standard, it is likely to remain the
interface of choice for most instruments well into the future. Even
many newer devices that connect to a PC through a USB port are shipped
with drivers that emulate a standard RS232 COM port so that they
remain compatible with traditional RS232 communication software.
The problem with RS232 communications is that it requires a hard
wired, point-to-point cable connection that is limited in the distance
that you can run a cable. You must also run a separate cable connection
to a unique RS232 serial port on a PC for each instrument that
you need to communicate with. This means that if you want to connect
multiple devices to a single PC, you must install multiple RS232
serial ports on the PC. Not only can this get messy, it also makes
it difficult to interface an instrument to more than one computer.
If the RS232 standard were to be improved upon, it would allow
multiple connections through a single cable, there would be no
restriction on the length of the cable and it would remain 100%
compatible with all currently available serial communications software.
Fortunately there is a very simple way to accomplish all of the
above improvements (and more) using currently available and reasonably
inexpensive hardware or software (TCP-Com). The trick is to use
a RS232 to TCP/IP converter (like TCP-Com or a hardware based “serial
device server”) to convert the RS232 serial connection to
a TCP/IP network connection. You would then be able to use an existing
Ethernet network as the backbone for connecting all the RS232 instruments
to all the PCs in a network.
You could use either a small hardware device called a “Serial
Device Server” or you could use our TCP-Com software to exposes
the serial ports on a PC to a TCP/IP network. TCP-Com essentially
allows you to use a PC as a serial device server.
The way that it works is that you use your existing network instead
of running RS232 serial cables and then connect the RS232 serial
instruments directly to the network using an appropriate (hardware
or software) converter. A hardware based serial device server is
a small box that has a RS232 serial port on one side and an Ethernet
connector on the other. It is basically a small computer that establishes
a network connection and then feeds any data that it receives through
the RS232 port out over the network connection through a TCP/IP
port and vice versa. The hardware device servers must be plugged
into the network through a hub or switch using standard network
cables. In most cases, the TCP/IP network protocol is used to pass
data across the network to other workstations. This means that
each device server would need to be configured with a unique IP
address just like each PC that is connected to a TCP/IP network
has its own unique IP address. The serial device server thus becomes
just another node on the network.
TCP-Com is a program that you run on a PC to expose the serial
ports on that PC to the network. In other words, it does the same
job as a hardware based serial device server except that it is
a software program that you run on a PC. You still connect the
instrument to a RS232 serial port on the PC, however the PCs network
connection is used to share the serial ports on that PC with other
workstations in the network. The IP address of the PC where TCP-Com
is running is used for all of the exposed serial ports on that
PC and you configure TCP-Com to feed data from each serial port
through a different TCP/IP port.
To make everything work transparently with existing software,
you would also need the ability to create a “Virtual COM
Port" on every PC in the network that needs to communicate
with each RS232 device. The "Virtual COM Port" tricks
your PC into thinking that the serial port on the serial device
server (or TCP-Com) is actually a serial port installed locally
on your PC. In other words, the “virtual” serial port
behaves just like a real serial port except that it actually establishes
a TCP/IP connection through the network to the serial port on the
serial device server. Any existing software that is designed to
open a standard RS232 serial port would then be able to open the
serial port on the serial device server just as if it were a serial
port installed directly in your PC. You can think of it as using
your network as an RS232 serial cable. Not only do you gain access
to all your RS232 instruments from any PC connected to your network
(or across the Internet if configured correctly), you do away with
having to run cables directly from a device to a specific PC. If
you use hardware based serial device servers, none of the PCs that
you might want to use will need any RS232 serial ports at all.
In addition, with the right software or hardware, more than one
workstation can communicate with the same RS232 device simultaneously
- something that is not possible with RS232 devices that are connected
directly to a PC.
Note: Some hardware based Serial Device Servers
come with Virtual COM Port drivers however for the ones that
do not , TCP-Com can
be
used to provide the virtual COM port functionality.
TCPCom is a software based "Serial Device Server" that
also has the ability to create Virtual COM ports that connect to
Serial Device Servers. In other words, it can act as both a serial
device server and as a Virtual COM port driver or "redirector".
For more information on TCPCom or to download a fully functional
demo version, please visit: http://www.taltech.com/products/tcpcom.html
See Also:
Sending and receiving serial data over the
Internet
A Very Basic Overview of TCP/IP
Communications
Resources:
Hardware Based Device Server Manufacturers:
Digi International:
Tel: (952) 912-3444 or 877-912-3444
http://www.digiboard.com/products/externalserialservers
(See the Digi One Realport Product on the Digi web site)
Lantronix
Tel: (800) 526-8764 or (949) 453-3990.
http://www.lantronix.com/products/ds/index.html
Tibbo
http://www.tibbo.com Precidia
Tel: 613-592-7557
http://www.precidia.com/
Links to other hardware vendors
Software Tools
TCP-Wedge
TCP-Com
WinWedge (Software Wedge for
Windows)
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