第十四章单元测试
- N: N network is based on RS485 transmission standard. There must be one PLC as master station and other PLCs as slave station. The total number of stations in the network should not exceed 8. The communication protocol of the network is fixed: half duplex communication is adopted, and the baud rate (bps) is fixed at 38400 bps; the data length of 7 bits, even check, stop b98. True or false (2 scores): Besides programming port, PLC of FX series has no built-in communication port, so it is necessary to insert RS-485 communication interface board into the interface of special function expansion card to expand its communication function. The interface board model PLC of FX3U series is FX3U-485-BD with the maximum extension distance of 50m.（ ）
- If the PLC of each station on the network has completed the setting of network parameters, after the network connection is completed, the working power supply of each PLC is turned on. It can be seen that the SD led and RD LED indicator lights on the communication board of each station are on / off alternately, indicating that the n: n network has been successfully established.（ ）
- The configuration of N: N communication network of FX or H2U system is mainly realized by setting network parameters by programming for PLC of each station. The programming is very simple. In step 0 of the program, M8038 can be used to write the corresponding parameters to the special data registers D8176-D8180 of the master station, and the station number of the slave station register D8176. However, it must be ensured that this program is written from step 0 as the N: N network parameter setting program and ends when any instruction or device that is not part of the above program is executed. This program segment does not need to be executed. It becomes effective automatically when it is programmed into this position.（ ）
- It is one of the methods to implement the engineering task that the man-machine interface configuration is carried out first, then the PLC programming data is planned and the program is further compiled. Its advantage is that the man-machine interface has passed the simulation test, and the data object of the real-time database provides a certain basis for the planning of PLC network variables and intermediate variables, which makes the planning more intuitive and operable.（ ）
The communication board is equipped with terminal resistance switch. For non-terminal stations in the network, the switch should be set to the OPEN position; For terminal stations in the network, the switch should be set to 330 Ω or 110 Ω.
A:对 B:错
答案:对
A:错 B:对
A:错 B:对
A:对 B:错
A:对 B:错
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