This circuit simulates termination and biasing of common RS485 networks. The diode serves as communication identificator.
The 150ohm resistor in the middle with 1.2k resistors coupled with hard 5V voltage source should match common cables with specific resistance of 120R. Propagation delay may be observed which is common in drivers like MAX487. 150R resistor should handle at least 150mW of power dissipation.
