RS485 undriven line reads 0
RS-485 has a defined differential voltage at both mark and space. The idle state is when voltage V_diff is -0.2V &lt; V_diff &lt; 0.2V; this is done by putting the transmitter in a Hi-Z state, usually by controlling the RTS signal from the UART. RTS is then used to turn on/off the transmitter, from Hi-Z to the defined voltage level for mark/space.