I have experience utilizing Python 2, however, it is important to note that Python 2 and Python 3 may not be completely interoperable. To demonstrate this, I have modified the final lines of the code example provided below:
Snippet:
import socket
server_address = "192.168.1.191"
server_port = 2000
client_socket = socket.socket()
client_socket.connect((server_address, server_port))
client_socket.send(b"hello")
Hello Thomas_v2,
I was able to resolve most of the errors, but I am still experiencing an issue where the data I send (in this case, "hello") is not being written to the database. The "RecvDaten" field remains blank. Do you have any insights on what could be causing this issue?
Thank you in advance for all your help! Your assistance has been invaluable to me.
Ensure to review the "LEN" parameter in your PLC program's TRCV call to determine the number of bytes being received. Data will only be copied into the specified "DATA" area if this parameter matches the number of bytes received. For example, I have used 5 as the value for "LEN" in my program because the string "hello" consists of 5 bytes.
Hello Thomas! I followed the steps in the blocks to capture the screenshots, and I believe everything is correct. Thank you!
Hi Thomas_v2, I just wanted to express my gratitude for your help in successfully completing the data switch. Now, I have a new question - is it possible for the PLC to send the data instead? Your assistance has been invaluable, thank you!
When a client connects or specific data is received, you can utilize the TSEND function in your Python script to send data back. In the example displayed in the accompanying screenshot, the TSEND function is triggered if the initial two characters received are 'h' and 'e'. This action results in sending the first 5 bytes of "SendData".data back, which may be 'world'. Therefore, if you send "hello" using your Python script, you should expect to receive "world". The code snippet for this functionality is as follows:
```
sock.send(b"hello")
print("SENT hello")
data = sock.recv(5)
print("RECEIVED:", data)
```
It is important to note that this example lacks error handling. Developing robust TCP communication programming is crucial in order to effectively address various potential issues that may arise.
Hello Thomas_v2, I need to specify the number of characters to be transmitted in the TCON block of my previous posts. How many characters should be included when sending or setting an amount? Thank you!
Is it possible for me to read data with a WORD instead of a PLC using a CHAR? Thank you for your help!
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Explore the features and consult the documentation to enhance your understanding. It is advisable to organize the information you wish to transmit into a struct within a datablock. This struct can then be utilized as a parameter for the Tsend function. In Python, convert the data into Python types using unpack. Remember, the S7 system operates in big endian. Refer to the enclosed PDF for a demonstration on converting a struct with a Word (2 Bytes), an Int (2 Byte), and a Real (4 Byte) value, totaling 8 bytes for transmission and reception.
Hey Thomas_v2, I need to transmit a value x from my Python script to the PLC. Will the PLC read this value as a Word or Int? Appreciate all your help thus far!
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If you are looking to communicate with Step7, Snap7 is the perfect library for the job. Explore more about Snap7 at http://snap7.sourceforge.net/ for seamless integration and streamlined operations.
I have found that HibonelessSnap 7 does not meet my needs, so I am in the process of developing my own system. Nonetheless, I appreciate the effort, thank you!
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Hello Thomas_v2, when sending a string to the PLC, it assigns the value to a variable of type INT or WORD instead of CHAR. Is there a way to change this to be in CHAR format?
If you're looking to transmit a character array to a PLC and convert it into an integer value, the first step is to convert the char array into a string. A handy library function called "Chars_TO_Strg" can help with this conversion. Next, utilize the "STR_VAL" function to convert the string into an integer, ensuring that the string contains valid characters for an integer. Working with strings in a PLC can be more challenging compared to languages like Python. I recommend sending binary integer values directly from your Python script to the PLC for a smoother process.
Hello Thomas_v2,
I apologize for the delay in responding as I have been heavily involved in this project. I need to transmit an integer value from a Python script to the PLC using more than one character. For example, Python should send the value 123456 to the PLC.
Thank you!
To establish a connection, utilize a socket and transmit data with the command: sock.send(b"123456"). This data will then be received as a character array in your programmable logic controller (PLC), which can be easily converted into the necessary datatype. It may be confusing why Python and sockets are being used if you lack expertise in Python programming and TCP socket fundamentals.
Hello Thomas_v2, I am familiar with Python but haven't connected it to a PLC before. I am unsure if I need to make any changes in Python to receive an Int in the PLC. The current project only supports Python, so I want to ensure compatibility. Thank you for your help!
Unfortunately, I have experience using Python 2, but have encountered compatibility issues between Python 2 and Python 3. In the code snippet provided, I attempted to establish a connection with a specific IP address and port using the socket library in Python. However, I received a "ConnectionRefusedError" with the message "No connection could be made because the target machine actively refused it." This error occurred while using TIA v14, a LAN cable, a Siemens CPU 1214C DC/DC/DC, and the Thonny 3.2.6 IDE for Python code.
To resolve this issue, it is recommended to check the network settings, ensure that the target machine is accepting connections on the specified port, and troubleshoot any potential firewall or security settings that may be blocking the connection.
In a recent statement, Bhargav Patel encountered an error message while working on a Python script. The message read: "ConnectionRefusedError: [WinError 10061] No connection could be made because the target machine actively refused it." Patel seeks a solution to this issue and asks for assistance. He mentions using TIA v14, a LAN cable, and a Siemens CPU 1214C DC/DC/DC. It is important to verify if the CPU has the same IP address as the example (192.168.1.191) and to check for successful pinging of the IP address. Additionally, it is recommended to examine the status value returned from the TCON block in the S7 program to troubleshoot the problem effectively.
When encountering the error message "Traceback (most recent call last): File "D:\BHARGAV PATEL\DOC\Temp\python\6mar_pypl.py", line 6, in sock.connect((address, port)) ConnectionRefusedError: [WinError 10061] No connection could be made because the target machine actively refused it," it indicates that there is no device on the internet at TCP/IP address 192.168.1.191 listening on port 2000. This error suggests that the system running Python can reach the 192.168.1.x or 192.168.x.x network via an ethernet interface that believes it is part of that network.
To resolve this issue, more information is needed. Please provide details such as the hardware, software, and network configuration of the PC running Python. If it is a Windows system, sharing the output of the command "ipconfig /all" would be helpful. For Linux systems, the output of "/sbin/ifconfig -a" is required. Additionally, sharing the output of the command "arp -a" is recommended.
Furthermore, it is essential to understand the network configuration of the PLC to which the python script is attempting to connect. This involves finding the Mac address on the hardware and determining its TCP/IP address assignment in the TCP/IP router's DHCP web page.
If you are unfamiliar with this terminology, seeking assistance from a network administrator may be necessary. Remember, some devices may ignore the source TCP/IP system running the Python script, so troubleshooting with the aforementioned steps is crucial for resolving the issue.
Can you provide further information on the functions Tsend and TRecv? Explore how these functions work and their significance in data transmission.
I have legacy code from an S7-300 PLC that utilizes Tsend and Trecv functions for UDP communication. This code was designed for an S7-300 PLC with an integrated Ethernet port. I created two Function Blocks, one for reading and one for writing.
Tsend and Trecv functions are essentially the Siemens S7's equivalent of socket commands. The issue with my code is that it combines LD and STL, making it incompatible with newer S7-1200s or S7-1500s due to differences in the STL.
I also implemented a unique 16-byte header for the UDP transfer, ensuring that all data is properly word or dword aligned, unlike Modbus TCP. This code, available at the URL https://deltamotion.com/peter/S7/Pndp-udp.zip, was only used a few times before being overshadowed by Profinet technology.
- 25-12-2024
- Peter Nachtwey
What operating system do you have? Have you tried using Node-Red for your projects? I recall there being an S7 connector available. Modbus support is definitely there - I've personally utilized it. Best of luck with your endeavors! -Yosi
How can I establish communication between a Delta PLC equipped with Ethernet support and Python using the PyModbus library? I am currently engaged in a project involving a Delta PLC and utilizing the Modbus TCP/IP protocol for connectivity. My initial test is being conducted with a Delta DVP-12SE11R PLC, where I have successfully interfaced with a modbus slave simulator using a Python code written with the pymodbusTCP module.
I have verified the functionality of the code by reading and writing necessary registers on the simulator. Now, my inquiry pertains to the process of connecting a physical PLC hardware to a PC, providing the PLC's IP address and port number to the Python code, and initiating the reading and writing of specified registers as outlined in the code.
In this implementation, I am utilizing the following code snippet:
```python
from pyModbusTCP.client import ModbusClient
c = ModbusClient(host='localhost', port=9999, auto_open=True)
regs = c.read_holding_registers(403705, 1)
print("Reading register values...")
if regs:
print(regs)
else:
print("Error")
print("Write value to register")
a = int(input())
c.write_single_register(403705, a)
```
By incorporating the aforementioned code into my project, I aim to seamlessly facilitate data exchange between the Delta PLC and Python environment via Ethernet connectivity.
Thomas_v2 mentioned that there are three potential methods to establish communication with an S7-1200 PLC. The first option involves utilizing a raw TCP connection, where configuration and programming of communication functions on the PLC side are necessary. On the Python side, the standard python sockets can be used, but it is important to consider TCP stream and endianess differences in Siemens PLCs.
The second option entails using the native S7 protocol along with an additional communication library on the Python side. An example of such a library is the python-snap7 library. However, this method only provides access to non-optimized datablocks in the S7-1200.
Lastly, the third option involves using Modbus TCP. To implement this on the PLC side, modbus function blocks need to be programmed. On the Python side, a modbus TCP library will be required. If you are interested in proceeding with the third option to establish communication with a PLC using modbus TCP in your Python code, please refer to the aforementioned steps.
Inquiring about how to communicate with a PLC using Python code and Modbus TCP as the third option? Look no further. By utilizing the MB_SERVER block from the Siemens library on the S7-1200, you can access the data area at the MB_HOLD_REG parameter. This enables you to interact with the data in your Python program using a Modbus TCP client library such as PyModbus with holding registers. One drawback to keep in mind is that the MB_SERVER allows the Client to read and write the process image of the S7-1200 by default.
Analyze the snap solution Thomas shared for efficient data transmission. Avoid using TSEND and TRECV as it would require duplicating Ethernet code on both the PLC and Python platform. Python enables data transmission in different formats, but lacks support for structures like C. To work around this limitation, pack data in Python to create headers or learn how to unpack data for header extraction. While sending a basic text message is straightforward, implementing functional data transfer can be challenging.
- 25-12-2024
- Peter Nachtwey
DiegoE expressed gratitude to Thomas_v2 for helping him successfully change data. Now, he wonders if it is possible for the automation to send the data instead. Thank you so much!
Discover Pylogix, a comprehensive tool designed for TCP communication with Programmable Logic Controllers (PLCs) using Python. This open-source software includes functionalities for reading and writing data from Allen Bradley Compact/Control Logix PLCs. Pylogix also features an active Discord community, providing support and collaboration opportunities for users. Explore Pylogix on GitHub to leverage its capabilities for your PLC projects.
Thank you for your input, however, this discussion is focused on Siemens products. Please note that pylogix is specifically designed for use with Allen-Bradley equipment only.