Universal RS485/422
Distributor
RS485 is very similar to RS422. So much so that it often causes confusion. Both are multi-drop, and both can communicate via very long distances, so then why choose one over the other? First of all, RS485 is generally a 2-wire system, although some manufacturers may specify 4-wire RS485, which is far less common and very similar to RS422 protocol. It is important that you identify which one is being employed when considering an instrument. Here are some main differences between 2-wire RS485 and RS422:
- RS485 can have multiple Commanding Devices and multiple Listening Devices. RS422 can have only one Commander and multiple Listeners. For example, you can connect one PC (the Commanding device) to 10 temperature controllers (listeners). The PC can instruct any of the controllers to change setpoint, or to send a temperature reading, but none of the controllers can command any of the other controllers. With RS485, you can have multiple PC's and multiple controllers on one bus, so that one PC can send a command to change a setpoint,and another PC can send a command to send back data, etc. Remember that all devices on the bus must have a unique unit address, so that only the addressed unit will respond. (similar to RS422)
- RS485 pinout wiring is easier since you are only dealing with 2 wires instead of 4.
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