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?