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PLC A U T O M A T I O N . . . . A P P L I C A T I O N N O T E S
Project: RS-232 to RS-422 Host Link Communications to Omron PLCs
Overview: Although all of Omron’s PLCs offer some form of a standard RS-422 serial port option, in some situations you will be force to convert an available RS-232 serial port for RS-422 communications.This note will provide information that will allow you to make the best possible product selection when needing to convert RS-232 to RS-422 for Host Link communications from PC to Omron PLCs.When doing so it is necessary to always operate in four wire RS-422 mode.
Listed below are three different converters that can be used on the PC side of the communications.All have been tested and work with the Omron PLC hardware listed below.
Option 1 NT-AL001 (Omron) – Is DIN-Rail mounted.Connector for the RS-232 side is a standard DB9 connector with custom pin out and RS-422 side is a removable terminal block.The only disadvantage is the need for a 5 VDC power supply that is connected through the DB9 connector of the converter. ($175.00)
Option 2 ADAM-4520 (Advantech) – Can be DIN-Rail or panel mounted. Connector for the RS-232 side is a standard DB9 used with a standard serial male to female cable and the RS-422 side is removable screw terminals.Power is 10-30 VDC connected on RS-422 connector.The only disadvantage is the need to remove the entire case to set configuration dipswitches. ($130.00)
Option 3 422PP9TB (B&B Electronics) – Converter can be mounted directly to the PC serial port with a screw terminal connector for the RS-422 side.Power is 12 VDC connected on RS-422 terminal block.The only disadvantage is the fact that B&B Electronics is a third tier vendor. ($74.95)
The following tables list the different types of PLC CPUs and communication ports used for the test, and the different converters used to convert from RS-422 back to RS-232.The converters are listed in order from best option to last resort.For those situations where it is necessary to use a cable along with the converter, I have included a cable recommendation or a wiring diagram.