Electronic – Using RS-485 receiver with RS-422 signals

rs422rs485

I have a controller that has a RS-422 output.

Can I use it to only send data to another device that has RS-485?

Best Answer

RS-422 & RS-485 are similar in that they both use balanced, differential signalling. All of the RS-422 & RS-485 systems that I have seen or worked with use 5V levels.

A RS-422 driver is an output-only device. It will happily feed a RS-485 device so long as that RS-485 device is only ever receiving data. You will have a data collision if the RS-485 device ever tries to transmit on that pair.

The best way to think of this is that RS-422 is intended for systems that use separate Tx & Rx signal paths. That is: there is a single sender on each of the two data pairs (one sender at each end of the link).

Note that RS-422 can have multiple listeners.

RS-485 is designed for multi-drop systems where multiple devices can talk and listen to the same single conductor pair.