Turbine equipment controller module DS200DCFBG1BKC

1. Asynchronous communication and synchronous communication:

In serial communication, the transmission rates of the receiver and sender should be the same, but there is a slight difference between the actual transmission rate and reception rate. If no measures are taken, errors will accumulate and cause misalignment when continuously transmitting a large amount of information, resulting in the receiver receiving incorrect information. To solve this problem, it is necessary to synchronize the sending and receiving processes. According to different synchronization methods, serial communication can be divided into asynchronous communication and synchronous communication.

Interface standards for serial communication:

1. RS-232C

RS-232C adopts negative logic, with -5~-15V representing logic state “1” and+5~+15V representing logic state “0”. The maximum communication distance of RS-232C is 15m, and the maximum transmission rate is 20Kbit/s. It only performs one-to-one communication. OYES PLC modules generally use 9-pin connectors, which only require 3 wires when in close proximity (one computer TD port to transmit to the PLC RD port, one PLC TD port to transmit to the PLC RD port, and one computer GND port to connect to the PLC GND port). RS-232C uses a single ended drive and receive circuit, which is susceptible to potential differences on the common ground and external interference signals.

2. RS442A

RS442A adopts balanced driving and differential receiving circuit. Using the voltage difference between two wires to transmit signals. These two wires are called A and B. When the voltage of B is higher than that of A, it is considered that a logic “high” level signal is being transmitted; When the voltage of B is lower than that of A, it is considered that a logic “low” level signal is being transmitted. The differential voltage range that can work effectively is very wide, from a few tenths of a volt to nearly ten volts.

3. RS-485

RS-485 is a variation of RS-422A, RS485 is half duplex, with only one pair of balanced differential signal lines, and cannot simultaneously transmit and receive signals. A serial communication network can be formed using RS-485 communication interface and twisted pair cables. Forming a distributed system, there can be 32 stations in the network.

The PPI, MPI, and PROFIBUS-DP protocols supported by the S7-200 module are based on RS-485 hardware. The communication interface of the S7-200 PLC module is a non isolated RS-485 interface with a common mode rejection voltage of 12V. For such communication interfaces, the signal ground potential between them is very important, and it is best to link their signal ground reference points together without necessarily grounding them. When networking S7-200 PLC modules, all sensor power terminals output by OYES PLC modules should be connected with wires. The M terminal is actually the 0V reference point for the A and B line signals. When communicating between the S7-200 PLC module and the frequency converter, all communication ports of the frequency converter should be connected to the M terminal and connected to the M terminal of the sensor power supply on the CPU.