Modbus is one kind of protocols that machine can transfer data through this method. Generally speaking, MODBUS is to machines what language is to human beings. Communication protocol is software level protocol, and different devices exchange data through the same protocol. Then machine needs physical port to transfer data, such as EIA 485(RS485)、EIA422(RS422)、EIA232(RS232) or RJ45 Ethernet.
Attention：Device with RS485 port does not mean it must support Modbus Protocol. Please contact Device provider for more information.
1.Different device provider has different sign：
RS422 4 wires
RS485 2 wires
| Transmit D+
1. Make sure the principle of connection is correctly when do wiring, and do not use T type wiring method, star type wiring method or any other wiring method for convenience.
2. Keep away from high noise source when wiring. Do not use the same groove as the power wire uses in the distribution box. Externally, keep as far away as possible from devices which have electric magnetic radiation. The transfer wire need to use shielded twisted par wire. Normal twisted pair wire can be used when conducting short distance communication in low noise environment to reduce cost. But in high noise environment, long distance communication or in case of high communication quality is required, the dedicated transfer wire for RS-485 is recommended. It may make higher budget, but the communication quality will be improved magnificently.
3. Terminal resistances must be parallel connected to the two terminal points of the whole communication circuit. For the twisted pair wire used by RS-485 interface, the terminal resistances should choose 120 Q 1/2 W ones.
Final check before transmitting data
1. Check whether the communication software is working properly, including whether the communication parameters (such as ID, baud rate, check bit, delay, time-out setting) are correctly.
2. Reduce environmental interferences.
3. Re-wire the transfer wire, and avoid noise source.
ID：ID can only be identical.
Baud、Parity Check Bit：Ever part of system setting should be same.
Delay Time：Short delay time interval may cause data lose.
Time out：1000~500ms are recommended, depending on devices.
If everything on the system is done correctly and communications still do not work, please contact PLC provider for more PLC communication setting details.