Max 485 auto transmission
First of all the 0ohm resistor is strange... But I will explain the circuit's functionality after considering this resistor as not connected
the NC is considered to be a wire. This is the only way the circuit will actually work. I have seen similar circuits before




when no data is being sent, TXD2 is idle and hence will equal to 5V (TTL UART ideal state)
5V on the npn transistor will yield 0V on its collector, that is RE_bar and DE. which means that the receiver is enabled and transmitter is disabled, which is exactly what we need. MAX485 will now convert whatever on the bus to the RXD2 wire.
when data is being sent, we have 2 cases: sending a logical 0 (0V) and logical 1 (5v):


a. when 5V is sent, as explained before, the transmitter is disabled, and A and B outputs are in high-impedance. But because of pull-ups and pull-downs on the A and B wires, A will be 0v, and B will be 5V which is a logical 1 RS485 signal. So it is "like" sending data except that the pull-ups and pull-downs are the ones driving the bus and not the max485 transceiver.

b. when 0V is sent, the transistor switches off. The transmitter is enabled, and 0V gets into DI. which outputs a 0V RS485 signal on A and B lines (that is A:5V , B:0V)