snap7

Siemens S7 PLC Communication with Snap7

This directory contains a collection of Python scripts designed to interact with Siemens S7 PLCs (Programmable Logic Controllers) using the python-snap7 library. These scripts provide examples for various operations such as reading from and writing to PLC memory, testing connections, and more.

Scripts Overview

Below is a description of each script found in this directory:

memory.py

This script defines a Python class S71200 which simplifies interaction with an S7-1200 PLC.

• Purpose: To provide a higher-level abstraction for reading and writing various data types to different memory areas of an S7-1200 PLC.
• Class: S71200(ip, debug=False)
  • ip (str): The IP address of the PLC.
  • debug (bool, optional): Enables debug printing if set to True.
• Methods:
  • getMem(mem, returnByte=False): Reads data from a specified memory location.
    • mem (str): The memory address (e.g., 'MX0.0', 'MB0', 'MW0', 'MD0', 'FREAL0', 'QX0.0', 'IB0').
    • returnByte (bool, optional): If True, returns the raw byte array; otherwise, returns the parsed data type.
  • writeMem(mem, value): Writes data to a specified memory location.
    • mem (str): The memory address.
    • value: The value to write (appropriate for the specified memory type).
• Supported Memory Areas:
  • M (Merkers / Memory Bits)
  • Q (Outputs)
  • I (Inputs)
• Supported Data Types: Boolean (bit), Byte (int), Word (int), DWord (int/dword), Real (float).
• Example: The script includes a commented-out example section (if __name__=="__main__":) demonstrating how to use the S71200 class to read and write to PLC memory.

snap7-PLC-test.py

This script provides functions to read and write to the Merker (MK) memory area of a PLC and includes a test case.

• Purpose: To test basic read and write operations on a PLC's MK memory area.
• Functions:
  • ReadMemory(plc, byte, bit, datatype): Reads data from a specific address in the MK memory area.
  • WriteMemory(plc, byte, bit, datatype, value): Writes data to a specific address in the MK memory area.
• Example: The if __name__=="__main__": block connects to a PLC, reads a bit from memory address MK100.2, attempts to write to it, and prints the status.

snap7-client.py

A simple client script to read real values from different memory areas of a PLC.

• Purpose: To demonstrate connecting to a PLC and reading floating-point numbers from the MK (Merker), PA (Process Image Output), and PE (Process Image Input) memory areas.
• Operation: Connects, reads a 4-byte real value starting from address 0 in areas 0x83 (MK), 0x82 (PA), and 0x81 (PE), prints these values, and disconnects.

snap7-read-write.py

This script demonstrates reading and writing a real (floating-point) value to the MK memory area of a PLC.

• Purpose: To provide a clear example of reading and modifying a real value in the PLC's memory.
• Functions:
  • ReadMemory(plc, byte, bit, datatype): Reads data (focused on MK area due to areas['MK']).
  • WriteMemory(plc, byte, bit, datatype, value): Writes data (focused on MK area).
• Example: The script connects to a PLC, reads a real value from address 0 of the MK area, writes the value of Pi (3.141592) to the same location, and then reads it back to verify the write.

snap7-test-connection.py

A very basic script to test the network connection to a PLC.

• Purpose: To quickly verify if a connection can be established with the PLC at the specified IP address.
• Operation: Attempts to connect to the PLC, prints whether the connection was successful, and then disconnects.

snap7-write-input.py

This script demonstrates reading from and writing to the Process Image Input (PE) area of a PLC. Writing to inputs is typically used for simulation or forcing values.

• Purpose: To show how to interact with the PLC's input image table.
• Functions:
  • ReadMemory(plc, byte, bit, datatype): Reads data from the PE memory area (areas['PE']).
  • WriteMemory(plc, byte, bit, datatype, value): Writes data to the PE memory area.
• Example: The script connects to a PLC, reads a bit from input address 0.0 (e.g., I0.0), writes a '1' to it, and then reads it back to show the change in the process image.

Prerequisites

• Python 3.x
• python-snap7 library: This library is essential for communication with the S7 PLCs. It can be installed via pip:

  pip install python-snap7

• Siemens S7 PLC: You need access to a compatible Siemens S7 PLC (e.g., S7-1200, S7-1500, S7-300, S7-400) configured with an IP address on the same network as the machine running these scripts. The PLC should also be configured to allow PUT/GET communication from external partners (often a setting in the PLC's hardware configuration or protection settings).

Usage

1. Configure IP Addresses: Before running any script, you will likely need to modify the PLC's IP address within the script. Most scripts have a line like plc.connect('192.168.1.X', 0, 1) where '192.168.1.X' should be replaced with your PLC's actual IP address.
2. Run from Command Line: Open a terminal or command prompt, navigate to this snap7 directory, and execute the desired script using Python:

   python <script_name>.py

   For example:

   python snap7-test-connection.py

3. Observe Output: The scripts will print information to the console regarding their operations, such as connection status, data read, or confirmation of data written.

Note: Ensure your network configuration allows communication between your computer and the PLC on the necessary ports (typically TCP port 102 for S7 communication).