Text version of the page

Chapter 6: Selecting RS-485 Devices

When purchasing devices for an RS-485 system many pitfalls can be avoided by determining the device’s communications characteristics before the system design is complete. Knowing what questions to ask up front can save a lot of troubleshooting in the field. The following device characteristics are all things that should be answered in the system design stage. 1.Is the device configured for two-wire or four-wire systems? 2.Is a signal ground connection available? 3.Is the device isolated? Does it contain surge suppression? 4.What value bias resistors (if any) are used in the device? Are they accessible for modification? 5.Is the device terminated? Is it accessible for modification? 6.What is the device’s response time (turn around delay)? 7.What is the programmable address range of the device? 8.What baud rate, or range of baud rates, is supported? If possible it is often useful to have a schematic of the serial port of each device in a system. The schematic can provide additional information that may be useful in troubleshooting or repairing any problems in the data system. 36 RS-422/485 Application Note
© Copyright B&B Electronics -- Revised 2506 B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph 353-91-792444 – Fax 353-91-792445