The schematic diagram below show the circuit diagram of an RS232 to RS485 converter circuit. The  EIA-485 standard, a.k.a TIA/EIA-485 or RS-485, is a physical layer standard defining the electrical properties of electronic drivers and receivers using balanced digital signal which is capable of handling multipoint systems. The ANSI Telecommunications Industry Association/Electronic Industries Alliance (TIA/EIA) is the organization who publish this standard. Using  the EIA-485 standard in application made it possible to transfer data robustly over long distances with high electrical noise environments. This standard is  designed to allow multiple receivers to be connected in a linear, multi-drop configuration. These feature is very useful in industrial environments or  similar applications.

 

THREE WIRE RS232 TO RS485 CONVERTER circuit schematic