What is RS-232, RS-485 & RS-422?

The RS-232, RS-422 and RS-485 designations refer to interfaces for digital data transmission. The RS-232 standard is better known as a normal computer COM port or serial port (although Ethernet, Wire and USB can also be considered as a serial port). The RS-422 and RS-485 interfaces are widely used in the industry for connecting various equipment.

The main differences between RS-232, RS-422 and RS-485 interfaces

Transmitter Type -
RS232 & RS422 - Full Duplex
RS485 - Half Duplex (2 wire), Full Duplex (4 wire)
Maximum Distance -
RS232 - 15 mtrs (9600 kbps)
RS485 & RS422 - 1200 mtrs (9600 kbps)
Contacts in Use -
RS232 - TxD, RxD, RTS, CTS, DTR, DSR, DCD, GND
RS422 - TxA, TxB, RxA, RxB, GND
RS485 - DataA, DataB, GND
Max. Number of connected devices -
RS232 & RS422 - only one
RS485 - max 256

Information transmitted via RS-232, RS-422 and RS-485 interfaces is structured as a protocol

Address type

Bit Address - 0 and 1
8 Bit Unsigned INT Address = [0 to 256],
Signed INT Address = [-128 to 128],
16 Bit Unsigned INT Address =

Function Codes for Modbus - 
Modbus protocol defines several function codes for accessing Modbus registers. There are four different data blocks defined by Modbus, and the addresses or register numbers in each of those overlap.