Summary of problems in the process of tq2440 and Siemens S7-200 PLC free port communication

1. After installing the PLC programming software Step 7 microwin on Windows 7, can the communication between the programming software and the PLC fail?

Cause: Step 7 microwin does not support win7 very well

Solution: Install the Virtual Machine in win7, the XP system in the virtual machine, and step 7 microwin under XP

2. One-way data transmission: the PLC sends correct data to PC serial 1 (baud rate 9600), but two-way data transmission: PC serial 1 sends data to PLC first. After the PLC receives the data, an error occurs when I send data to PC serial port 1. Why is the data received by PC serial port 1 inconsistent with the data sent by PLC (baud rate 9600 )?

Cause: the baud rate is not set properly.

Solution: Increase the baud rate appropriately. The experiment shows that the baud rate is set to 115200 and can be received normally.

Note: The serial port RS485 on the PLC adopts the half duplex mode. The PC/PPI cable is used between the PLC and the PC. There must be a time interval between the PLC receiving and the PLC sending, the interval must be later than the switch time of the PC/PPI cable. When the baud rate is 115200, set the interval to 1 ms.

3. About RS232, rs422, RS485, half duplex or full duplex?

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