3 Summary

In summary, three scenarios are tested in this application note for two polarity free RS-485 transceivers – THVD1505 and SN65HVD888. After reviewing the test results, it is clear that the polarity-free devices should be put in the receiver mode as they are powered up in applications. After the biased bus makes the devices fix their polarities, the devices can work normally in the system. Again, if an existing RS-485 system is to be upgraded with this polarity free feature, some circuitry is needed to fix bus polarity. Like it is mentioned before, either pull-up and pull-down resistor network or a regular RS-485 transceiver (THVD1500, THVD1439, and so on) can do the job. With hardware upgrade, software update is not required.