Network Communications - multiport serial cards


Thread Starter

Tom Brickner

I would like some opinions about multiport serial cards. Presently I have a standard P.C. with Wonderware Intouch HMI software connected through an RS232 serial port to a Dutec RS232-RS485 (4 wire) converter, then connected to 25 Eurotherm Temperature controllers. The protocol I am using is modbus RTU. I need to expand my system to include 350 controllers (30 controllers per serial port)(approximately 13 ports) and want to find out what best options on the market are for PCI serial port cards. Presently I have looked at SIERRA MONITOR 8051 communications bridge with 8 RS232 Serial Ports and 2 RS485 Ports, MOXA Intellio C320Turbo Multiport Serial Card cabable of 128 RS232 Serial ports, and a WCSC 8 port RS232 multiport serial card. So far I like the Sierra Monitor because you can set it up in a redundant system and I also like the MOXA C320Turbo because of the cost. Does anybody like these serial cards, or have any others to recommend? I also wanted to know if it is ok to use an RS232 to 4 wire RS485 converter or is direct RS485-RS485 preferred?

Robert Willis

Tom: In addition to using a multiport serial card you could use a Modbus TCP/IP to Modbus Bridge and then use Ethernet for your network connection. Schneider Electric has a DIN rail mounted device that will meet your needs (Part Number: 174CEV30010. This device supports RS232 or RS485 on the serial port and 10Mb on the Ethernet Port. You can obtain information on this device at If you would like a rack mounted type of device, Niobrara Research and Development manufactures a module that will plug into a Schneider Electric TSX Quuantum backplane. The module is a QUCM-LE which includes two Serial ports capable of supporting RS232/RS422 or RS485. Their website is You can use either the Wonderware Modbus TCP/IP driver or the Standard Automation EFM manager to communicate to the Ethernet bridges. If you would like to dicsuss your application in greater detail please drop me a E-Mail. Regards Robert Willis Square D Company Senior Executive Field Application Engineer E-Mail: [email protected]

Theo Baarslag

Here we use the Etherlite series from digi (see for remote RS232/422 concentrators. I don't think they have an RS485-version, but it might be a nice alternative. These devices connect to 10/100BASE-TX networks, giving your computer 16 extra serial ports at a remote location. I am not totally happy with the power supply's, they seem not robust enough to me for life-span. KR, Theo Baarslag PLC-/CIMspecialist IAMS Europe bv, Coevorden

Crucius, Wesley

Check out the 4 and 8 port "terminal-server-like" serial port devices from Comtrol. I've used them successfully, and the solution is very scalable and distributable. Also, I like the products from Sea-Level systems for card based solutions.
Why not use Serial-to-USB? There are several companies that make 232-USB converters. The advantage is that you do not take up interrupts and you can easily expand to fit your needs.

Tom Brickner

Dear Gerry, Mr. Willis, Mr. Baarslag, Mr. Crucius, and Mr. Graham. I wanted to extend my thanks for all your responses. This gives me a few more options to look at. Thank you again. Sincerely, Tom Brickner