The use of optocoupler between the communication master chip (such as the single chip microcomputer) and the 485 interface chip can improve the anti-interference ability to a certain extent, because the optocoupler can isolate the electrical signal connection on both sides.
But in fact, optocoupler isolation can only block differential mode interference, and the main form of electromagnetic interference is common mode interference, optocoupler isolation has no effect on common mode interference. In order to improve the anti-interference ability, it is necessary to install some protection devices at the 485 port, such as common mode filters, electrostatic protection devices, tvs tubes, discharge tubes and so on.