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Entry type: FAQ Entry ID: 19449428, Entry date: 01/21/2015

How do you add a CPU as DP slave to the DP master system of a different CPU whereby the CPUs are configured in different STEP 7 projects?

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This entry shows how to add a CPU as DP slave to the DP master system of another CPU when each CPU has already been configured in a separate STEP 7 project.

In this example we show the configuration of a CPU 414-3 DP as DP master (STEP 7 Project 1). A CPU 315-2 DP is configured as I slave (STEP 7 Project 2) and added to the DP master system of CPU 414-3 DP. Consistent and non-consistent data is used for data exchange.

Project 1 includes the following hardware configuration.

Fig. 01

Project 2 includes the following hardware configuration.

Fig. 02

Configuring CP 315-2 as a DP slave

  1. Configure the CPU 315-2 DP as DP slave. For this you open the hardware configuration of Project 2.
  2. In the hardware configuration you open the Object Properties of the DP interface. In the "General" tab you click the "Properties" button. The "Properties - PROFIBUS DP interface" dialog opens.

    Fig. 03
  3. Network the CPU 315-2 DP with the PROFIBUS subnet and set the PROFIBUS address.

    Fig. 04
  4. In the Object Properties of the DP interface you open the "Operating Mode" tab. Select "DP slave" as the operating mode.

    Fig. 05
  5. In the Object Properties of the DP interface you open the "Configuration" tab. Here you define the input and output areas. Click the "New" button to create a new configuration line in which specify the address type and IO address as well as the length, unit and consistency of the IO data.

    Fig. 06

    To achieve consistent data transfer you set Consistency over Total length. To distinguish clearly between consistent and non-consistent data we have configured different data areas in this example (see Table 1).
  6. Save and compile Project 2.

Add CPU 315-2 DP (DP slave) to the DP master system of the CPU 414-3 DP

  1. The CPU 315-2 DP is added as DP slave in Project 1 by GSD file. The GSD file for the CPU 315-2 DP (article number: 6ES7315-2AG10-0AB0) is available in Entry ID 113652.

    Instruction for installing GSD files  are available in Entry ID: 2383630.
  2. After installation of the GSD file, the CPU 315-2 DP is located in the hardware catalog under "PROFIBUS DP > Other Field Devices > PLC > SIMATIC".
  3. Add this CPU in Project 1 to the DP master system of the CPU 414-3 DP and set the associated PROFIBUS address.

    Fig. 07
  4. When manually incorporating the DP slave you should make sure that the bus parameters and PROFIBUS address of the DP slave in both Project 1 and Project 2 are identical.
  5. Define the IO configuration of the CPU 315-2 DP in Project 1 with the modules available in the hardware catalog under "PROFIBUS DP > Other Field Devices > PLC > SIMATIC > CPU 315-2 DP".

    Fig. 08
  6. The IO data configuration in both projects must be exactly opposite. This means that the output data on the master becomes the input data on the slave and vice versa (see Table 1). You need the system functions SFC14/SFC15 or a process image partition (PIP) to transfer consistent data.

    Additional information about consistent data is available in the following Entry IDs: 11646774, 245111 and 5116353.
  7. Save and compile Project 1 as well and load both projects into the corresponding CPUs.
DP master DP slave
Type Length Consistency Type Length Consistency
Output 10 bytes Unit Input 10 bytes Unit
Output 2 bytes Unit Input 2 bytes Unit
Output 4 bytes Total length Input 4 bytes Total length
Input 15 bytes Total length Output 15 bytes Total length
Input 1 word Unit Output 1 word Unit
Table 01

This procedure for configuring a master/slave connection of two CPUs in different STEP 7 projects can be applied in principle for other CPU types.

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