RS-485 is an updated version of the RS-422 interface. It is designed to communicate between multiple devices connected to a single data line. Standard allows connecting 32 transceivers to the data line. This is achieved by using tri-stable drivers that are separately programmable. This allows only one device to work at a given time.
Resistors used in the circuit are so-called termination resistors for matching the transmitter and receiver impedances to avoid reflections. The matching resistor depends on the cable used but is 120Ohm.
Usually, RS485 chips have two control inputs Data Enable(DE) and Receiver Enable(RE):
On the IC, you see that DE active is high level and RE is low level. This allows connecting the control line to a single MCU pin. This assures that node won’t be receiving while it is transmitting:
In many cases, CAT-5 cable is used with an impedance of 100Ohm and terminations of 120Ohm resistors at both ends of transmitter and receiver. CAT-5 cable already has twisted pairs, and it is cheap enough to use for many applications.