# Why Use RS-485 or RS-422?

There are several advantages in using RS-485 or RS-422 interfacing on the Catalyst Modbus port. RS-485/RS-422 line drivers were designed to allow the transmission of data signals over considerably longer distances than allowed by RS-232C line drivers. Compare the maximum cable length of RS-232C, RS-485 and RS-422 below:

RS-232C | 50 Feet
RS-485 | 4000 Feet
RS-422 | 4000 Feet

Maximum Cable Length

This longer allowable cable length is due to fact that RS-485/RS-422 drivers and receivers operate in “differential mode” compared to RS-232C which uses “single-ended mode”. For each signal, such as transmitted or received data, differential signaling uses two complementary signals of equal and opposite polarity. Differential mode inherently has a much higher immunity to electrical interference and noise. Typically, RS-485 and RS-422 cabling uses twisted pair cable and frequently, shielded twisted pair cable.