Siemens S7 PLC Connection 

Introduction  

This report provides guidelines for establishing a connection to Siemens S7 PLCs, specifically focusing on the S1200 and S1500 models. To initiate a connection with the PLC, it is essential to verify and control access through the S7 connector, which communicates with the PLC via port 102.

Access Verification  

Before establishing a connection with the PLC, it is crucial to verify and control access using port 102 on the S7 connector. Once access is confirmed, specific information is required to establish a connection.

Connection Information  

• PLC Address

• Rack and Slot Information

Physical Connection  

Additionally, obtain the slot information where the PLC is physically connected.

IPI (Input Image): The Input Image represents the current state of all input signals connected to the PLC. It's a data structure where the status of inputs is stored. The IPI is updated by the IPU based on the signals received from input modules. The PLC's program logic typically references the IPI to make decisions and perform control tasks based on the external inputs.

In Siemens PLC programming, "EB" typically stands for "Input Byte". An Input Byte (EB) is a data type used to represent a group of digital inputs in the PLC's memory. It's a byte-sized memory location where each bit corresponds to a specific input channel.

When you refer to "Read/Write IPI (EB) from PLC," it likely means reading or writing to an Input Byte that represents the Input Image (IPI). The Input Image (IPI) represents the current state of all input signals connected to the PLC, stored in memory. By reading or writing to this memory location (Input Byte), you can access or modify the state of the inputs in the PLC program.

Here's a brief explanation of what each operation might entail:

Read IPI (EB) from PLC: This operation involves reading the current state of the Input Image (IPI), which is stored in an Input Byte (EB) in the PLC's memory. It allows you to retrieve the status of various input signals connected to the PLC.

Write IPI (EB) to PLC: This operation involves writing new values to the Input Byte (EB) that represents the Input Image (IPI) in the PLC's memory. By doing so, you can simulate or change the state of input signals within the PLC program.

These operations are commonly used in PLC programming to interface with input signals and make decisions or perform control tasks based on the state of the inputs.

IPU (Input Processing Unit): The Input Processing Unit is a hardware component responsible for processing incoming signals from various input modules. It interprets the signals received from the input modules and updates the Input Image accordingly. Essentially, the IPU serves as the interface between the physical inputs and the PLC's internal logic. It ensures that the PLC's program logic accurately reflects the state of the inputs connected to the system by continuously updating the Input Image.

In Siemens PLC programming, "AB" typically stands for "Analog Byte". An Analog Byte (AB) is a data type used to represent a group of analog inputs in the PLC's memory. It's a byte-sized memory location where each byte corresponds to an analog input channel.

When you refer to "Read/Write IPU (AB) from PLC," it likely means reading or writing to an Analog Byte that represents the Input Processing Unit (IPU). The Input Processing Unit (IPU) handles incoming signals from various input modules and updates the Input Image accordingly.

Here's a brief explanation of what each operation might entail:

Read IPU (AB) from PLC: This operation involves reading the current state of the Input Processing Unit (IPU), which is stored in an Analog Byte (AB) in the PLC's memory. It allows you to retrieve the status of various analog input signals processed by the PLC.

Write IPU (AB) to PLC: This operation involves writing new values to the Analog Byte (AB) that represents the Input Processing Unit (IPU) in the PLC's memory. By doing so, you can simulate or change the processing of analog input signals within the PLC program.

These operations are commonly used in PLC programming to interface with analog input signals and process them within the PLC's control logic.

Data Reading Configuration  

To read data from the PLC, it is necessary to configure input parameters based on the chosen function. Four functions are available for reading data from the PLC:

1. Read/Write Data Block

2. Read/Write Merkers (MB)

3. Read/Write IPI (EB)

4. Read/Write IPU (AB) (tested)

Read/Write Data Block  

For the Read/Write Data Block function, the following information is required:

• Data Block Address

• Byte Offset

• Bit Offset

• Data Type

Read/Write Merkers (MB), Read/Write IPI, Read/Write IPU (AB) (tested)  

For these functions, the following information is required:

• Address

• Bit Offset

• Data Type

Data Access  

Once all necessary information is provided, data can be accessed at the specified address.

Data Address

 Examples  

%DB5.DBW8

%DB5.DBD60 à Read DB Address:5 Offset: 60 Data Type: DINT

%DB1.DBD2 à Read DB Address: 1 Offset: 2 Data Type: DINT

Additional Configuration for Extended S7 Protocol  

The newer PLCs provide an "extended" version of the S7 Protocol, requiring additional configuration steps beyond the basic setup. Follow the steps below to ensure successful communication:

1. Disable Optimized Block Access:

• Navigate to the PLC configuration settings.

• Locate the "Optimized Block Access" option for the DBs you intend to access.

• Disable the "Optimized Block Access" for the relevant DBs. Refer to the provided image for guidance.

2. Enable PUT/GET Access in Protection Section:

• Access the CPU Properties in the PLC configuration.

• In the "Protection" section, find the "Permit access with PUT/GET" checkbox.

• Enable the "Permit access with PUT/GET" option. Refer to the provided image for guidance.

These additional configuration steps ensure compatibility with the extended S7 Protocol and enable seamless communication with the PLC.

https://github.com/robinson/gos7  

https://flows.nodered.org/node/node-red-contrib-s7