We can determine according to the electrical characteristics of RS-485: the logic \"1\" is expressed by the voltage difference between the two lines as (0.2~6) volts; The logical \"0\" is represented by the voltage difference between the two lines as -(0.2 to 6) volts. The interface signal level is lower than RS-232-C, it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which can be easily connected with the TTL circuit. So the 485 level is 0.2 to 6 volts.