Siemens S7-200 PLC how to control inverter operation through free port communication - News - Global IC Trade Starts Here.

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Photocoupler

1. How does S7-200 control the operation of Siemens inverter through free port communication?

1. The communication protocol of Siemens inverter is fixed. Such as A, A' format. To control the start-stop A' format of the motor, to change the operating frequency of the inverter, use the A format.

2. According to the communication protocol of Siemens inverter, S7-200plc sends data to the inverter through the free port to realize the forward, reverse, stop and modify the output frequency of the Siemens inverter.

Second, Siemens inverter communication protocol

Sum check calculation:

The ASCII code corresponding to the frequency value: the frequency data content H0000 to H2EE0 becomes 0 to 120 Hz in decimal, and the minimum unit is 0.01 Hz. If you want to represent the data 10Hz now, that is 1000 (unit is 0.01Hz), 1000 is converted into hexadecimal for H03E8, and then converted to ASCII code for H30H33H45H38.

Sum check code

The sum check code is two ASCII code numbers (hexadecimal) represented by the lowest byte (8 bits) of the sum (binary) of the checked ASCII code data.

Third, S7-200 free port communication

1, communication port control byte

2, send command XMT and receive command RCV

Description:

(1) Sending and receiving instructions can easily send or receive data of up to 255 bytes.

(2) PORT specifies the port to send or receive.

(3) TBL specifies the transmit or receive data buffer, the first data specifies the number of bytes sent or received.

(4) The interrupt can be called when the transmission is completed, and the interrupt can also be called when the reception is completed.

Fourth, the project is realized

The S7-200PLC free port communication mode is used to control the Siemens inverter, and the motor is driven to start and stop forward, and the operating frequency of the inverter can be changed. Set the inverter station number to 1.

The code for forward rotation start is: H05H30H31H46H41H31H30H32H38H31

The code to stop is: H05H30H31H46H41H31H30H30H37H46

The code to change the inverter output frequency to 20Hz is: H05H30H31H45H44H31H30H30H31H04H42H35

1, set the inverter parameters

2, write PLC free port communication control program

to sum up:

1. When communicating as a free port, you must first study the communication protocol and data format of the communication device.

2. When communicating for free port, if the PLC is required to send both data and receive data. It is necessary to coordinate the transmission and reception of both devices of the communication. Because for RS485 communication, it cannot be received when transmitting, and cannot be sent when receiving. This requires coordination with the timing interrupt and communication interrupt mechanism.

3, special memory (port 0)

SMB86 Receive Message Status Byte

SMB87 receives information control byte

The beginning of the SMB88 information character

SMB89 describes the end of the message character

The SMB90 idle line time period sets the most significant byte in milliseconds.

The SMB91 idle line time period sets the least significant byte in milliseconds.

The SMB92 intermediate character/information timer overflow value is set in milliseconds. If this period of time is exceeded, the reception of the information is terminated. Most significant byte.

SMB93 high and low valid bytes.

The maximum number of characters (1~255) to be received by SMB94.