Howdoesitwork?
The main feature of the RS422/RS485 interface is that the signals can be transmitted and
received at distances up to 1200m by using the so-called twisted pairs - basically, the signal and
its inverted copy are sent via the twisted pair wires. Because of the length of the twisted pair, it
will unavoidably be exposed to the influence of the EMI. The interferences will appear in both
wires of the twisted pair equally, but thanks to the opposite polarity of the signals the wires are
carrying, the interferences will get canceled at the differential inputs of the SN65HVD31. This
way, greater signal communication distances can be achieved than with the regular UART.
RS422/RS485 only specifies electrical characteristics of the transmitter and the receiver. It does
not specify or recommend any communications protocol, only the physical layer. The top layer
communication protocol of choice can be used, such as the MODBUS or DMX protocols.
To improve the signal stability, RS485 3 click is equipped with the TVS – transient voltage
suppression diodes used to protect the circuit from the static electricity discharges and other
types of dangerous electrical discharges, that might occur.
There are four onboard screw terminals (RX+, Rx-, Tx+, Tx-) for connecting RS422/RS485
twisted pair cable, along with two screw terminals (GND) for common ground connection.
TX and RX pins should be used for connecting MCU UART interface. Two resistors (R2 and
R5) should be unsoldered if using more than two clicks on the RS422/RS485 bus.
