图1 Set PLC communication parameters

COM port parameter settings：On this page, corresponding settings can be made for the communication parameters of the PLC. The default communication parameters for PLC serial port are: baud rate 9600, data bit 8, stop bit 1, and checksum NONE;

Serial communication protocol types：including Modbus master, Modbus slave, and Freeport communication, default protocol is Modbus slave;；

Station number：Set the station number of the PLC, and different COM ports can have different station numbers;

Timeout：This parameter only takes effect during Modbus master communication and has no practical significance for slave and free port communication. It represents the maximum waiting time for the PLC to receive one packet of data from the slave each time it communicates as the master, with a default value of 20 * 10ms;

Number of retransmissions：This parameter only takes effect during Modbus master communication and has no practical significance for slave and free port communication. It represents the number of retransmissions that will occur again when receiving data from the slave after timeout, with a default value of 3;

Buffer bit：This parameter only takes effect during free port communication and has no practical significance for Modbus master and slave stations. It indicates whether data is buffered in 8-bit or 16 bit format during communication;

Attention：

1. If you want to use MODBUS master communication, you must select the Modbus master protocol, establish and edit a Modbus master table, and use Modbus commands in the ladder diagram;

2. When the communication protocol of the COM port is set to MODBUS master or free port communication, it can no longer be used to download projects, nor can it be monitored. Only when the Modbus slave protocol is selected and downloaded to the PLC can it have download and monitoring functions;

3. In addition to downloading and updating serial port information through configuration information, settings for serial port baud rate, data bits, stop bits, checksum, station number, etc. can also be set through special registers D8066~D8075, M8184;