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www.instrument.com - Thursday, November 20, 2008
Printer-friendly version of the page "Serial EDAS"
(URL: http://www.edasce.com/rs232-ethernet-interface.html)
Remotely access RS-232 devices over your Ethernet!
Scales, terminals, printers, PLCs,
barcode scanners, instruments, and more
can be accessed right from your desk!
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Intelligent Instrumentation’s Ethernet/Serial Interface offers a simple and reasonably priced way to connect RS-232 devices directly to an Ethernet network. These new devices use the industry standard TCP/IP protocol, providing a non-proprietary communication link with virtually any type of host. Real-time communication between RS-232 devices and any number of networked computers, databases and applications is supported.
The Ethernet/Serial Interface features a compact, efficient design which is easily mounted in areas with limited space. A DIN-rail mounting option allows it to be mounted directly to walls, machinery, or the inside of a cabinet. Two models of the Ethernet/Serial Interface are available. The EDAS-1025E-1 features two bi-directional RS-232 ports, and the EDAS-1025E-2 has four ports.
Almost every facility uses at least one or several of these types of devices. Chances are, you do too. By connecting these serial devices to your Ethernet, you can easily share data with any number of computers and other resources on your network. This approach is much more convenient and economical than connecting each RS-232 device directly to a host system. The additional benefits of simplified wiring and centralized management saves time and money for everyone involved.
Open System
Serial EDAS units communicate over any Ethernet network (LAN) using industry-standard TCP/IP protocol, providing a non-proprietary interface to virtually any host. Each EDAS unit has a TCP/IP stack built-in and receives its own unique network IP address configured through one of its on-board RS-232 serial ports.
Operation
Unlike transceivers, repeaters or port multipliers, the Ethernet/Serial Interface is an intelligent device that performs more than just a physical connection or signal-forwarding function. It can be configured to communicate synchronously, so that it only responds to polling requests from a host. Alternately, it can communicate asynchronously, so that it automatically broadcasts data as it is received from a connected RS-232 device. You can configure it to recognize the correct terminator so that it knows when to send data, and you can have it send the data it receives from the connected RS-232 device to any host you designate.
OEM Version
Many OEMs (Original Equipment Manufacturers) are also realizing the benefits of integrating serial to Ethernet conversion into their products. You can provide your customers with a network-ready solution by embedding an Ethernet/Serial Interface directly into the serial devices you manufacture. By providing a simple way to link RS-232 devices to an Ethernet network, you add considerable functionality and value to your products.
"Board-only" versions of the Serial EDAS series are available for these types of embedded applications. These versions allow the circuit board to be mounted directly into your equipment. OEM Versions of the Ethernet/Serial Interface are powered from +5VDC for convenience.
EDAS-1025E systems act as application servers, providing remote RS-232 serial I/O to clients on the network. EDAS units are programmed over Ethernet via your PC or other computer using the Net Link software driver libraries (and your programming language) or through Windows 95 and NT based application generator software support libraries.
Through software support functions you can send or receive data to or from a unit's serial ports, send special control characters, check the status of a serial transmissions and program an alarm condition. The alarm functions can be used to detect receipt of special characters (carriage return/line feed, etc.), any character or a timeout condition. In response to the alarm condition, a user defined message or the serial input data can be sent to a remote host on the network or to another serial port on the EDAS unit. The detection of the alarm and transfer of data can be programmed to operate in synchronous or asynchronous modes. In synchronous mode, the status of the alarm must be polled by the client application to determine if the alarm has occurred. In asynchronous modes, the EDAS unit automatically sends specified data to the client (and or external serial device) when the alarm condition occurs.
The serial ports on EDAS-1025E units support software flow control (XON/XOFF), two hardware flow control modes (DTR/DSR, RTS/CTS), and two modem support lines - RI (Ring Indicator) and DCD (Data Carrier Detect). Software support provided through the above mentioned packages allow configuration of flow control methods and detection of flow control signal states. Packaged EDAS Ethernet/Serial Interface Units
Each serial port on EDAS-1025E-1, or EDAS-1025E-2 systems interface with any device which communicates via RS-232, including PLC's, controllers, instruments, scales, gauges, smart sensors, machines, terminals and scanners. The EDAS-1025E enables any of these devices to communicate with computers located anywhere on an Ethernet network. As mentioned previously, a wide range of supply voltages may be used to power the units. Also, by using the EDAS-1029A-1 DIN-Rail Mounting Kit, units can mounted on standard DIN-Rails. All ports support the following RS-232 lines: GRND, RX, TX, RTS, CTS, DSR, DTR, DCD, RI.
OEM Models
OEM models, EDAS-1025E-1G and EDAS-1025E-2G, are available to those who wish to incorporate this innovative design into a larger system. These "board-only" models are powered from +5 VDC and allow the circuit board to be mounted directly into your equipment. All ports support the following RS-232 lines: GRND, RX, TX, RTS, CTS, DSR, DTR, DCD, RI.
Serial Subsystem
The serial subsystem combines dual UARTS with +5V driven RS-232 transceivers to achieve a baud rate of at least 9600. Two or four RS-232 9-pin serial ports are available on the EDAS-1025E unit, depending on the model chosen. One of the RS232 serial ports (COM1) on the front panel is used for the initial configuration of the unit. Each port supports the standard RS-232 connections for 9-pin ports: GRND, RX, TX, RTS, CTS, DSR, DTR, DCD, and RI. A pin-out diagram is provided in Appendix A. Use of the control and status line signals RTS, CTS, DSR, DTR, DCD, and RI are dependent on the hardware and software implementation for your applications. Further guidance on these topics is provided in the Net Link software reference manual and in standard literature on serial communications.
Specific Considerations
The commands you issue to a device and how you exchange data with it varies from manufacturer to manufacturer. With the exception of many modems, there is not a commonly used serial device command set or "protocol". Typically, a device responds to a predefined set of ASCII command strings and sends res ult data back in a particular format. Special characters may also be used to specify the beginning and ending of a command or data sequence. The EDAS-1025E unit's software support packages, the Net Link Software Libraries (drivers), the EDAS Visual Designer Support Library and the EDAS LabVIEW library allow you to send and receive any ASCII or binary data.
Normally all devices start-up in receive or listen mode. Thus, there is little chance that a device will inadvertently activate the EDAS-1025E unit' s executive program on start-up. Never the less, it is good practice to configure this port early in your application and monitor for power down situations.
The maximum rate at which serial data can be successfully sent and received is constrained by several factors. These include the Baud rate(s) supported by the device, the cable length and quality, the noise environment and the overall processing load placed on the EDAS-1025E unit (which may include access from multiple clients and simultaneous analog I/O activities). Baud rates supported by an EDAS-1025E unit (and through support software) are: 300, 600, 1200, 2400, 4800, 9600, 14400, and 19200 bits per second. Higher Baud rates (38400, 57600 and 115200 bits per second) may be used, however, serial I/O errors are more likely. Other supported communication parameters include: even, odd or no parity, 7 or 8 data bits, 1 stop bit and flow control options "none", "XON/XOFF", "DTR/DSR" and "RTS/CTS".
Embedded Ethernet/Intranet communications for countless Serial (RS-232) devices such as:
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