http://
www.odotautomation.com
57 / 60
TEL:
+86-0816-2538289
interface circuit. RS422 adopts four-wire plus ground wire (T+, T-, R+, R-, GND),
full-duplex, differential transmission, multi-point communication data transmission
protocol. It USES a balanced transmission line that is unidirectional/non-reversible,
with or without an enabling end. Because the receiver USES a high input impedance
and the sending driver is stronger than RS232, it is allowed to connect multiple
receiving nodes on the same transmission line, up to 10 nodes. That is, one Master
device (Master), the rest are slave devices (Salve), and the slave devices cannot
communicate with each other, so RS-422 supports point-to-many two-way
communication.
The RS-422 has a maximum transmission range of 4,000 feet and a maximum
transmission rate of 10Mb/s. The length of the balanced twisted pair is inversely
proportional to the transmission rate, and the maximum transmission distance can be
reached only if the rate is below 100KB /s. The highest rate of transmission can be
obtained only over very short distances. Generally, the maximum transmission rate
obtained on 100 meters long twisted pair is only 1Mb/s.
The RS-422 requires a terminal resistance that is approximately equal to the
characteristic impedance of the transmission cable. In short distance transmission, no
final resistance is required, that is, no final resistance is generally required below 300
meters. The final resistance is connected to the farthest end of the transmission cable.
In a master multi-slave network connection, all the sending terminals of the slave
connect to the receiving terminals of the master station by daisy-chain. All the
receiving ends of the slave stations are connected by daisy-chain to the sending end
which is finally connected to the master station.
The RS422 pin definition:
RS422
（
9 Pin
）
Function
Remark
3
R-
Receive negative
Must connect
2
T-
Send negative
Must connect
7
R+
Receiving positive
Must connect
8
T+
Send positive
Must connect