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Entry type: FAQ Entry ID: 1016961, Entry date: 06/25/2004

Direct data exchange (internode communication) between two CPU modules

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How do I configure direct data exchange (internode communication) between two CPU modules configured as DP slaves?

Communication between two CPU stations configured as DP slaves and operated by the same DP master is called direct data exchange. The following configuration is implemented in the following sample project.

Fig. 1: Configuration of the sample project

First incorporate the three CPU stations in your STEP 7 project and link both slave stations to the master, then proceed as follows to configure direct data exchange:

  1. Go to the Hardware Configuration of the DP master.
  2. In the first slave station configure at least one row as data exchange for master-slave communication.

Fig. 2: Configuration of the CPU 315-2DP with DP address 3

  1. You should configure at least one slot with input data on the master and output data on the slave. This data will be "listened to" by the second DP slave.

Fig. 3: Master-slave configuration

  1. Switch to the configuration of the second DP slave in Hardware Configuration of the DP master.
  2. If you enter a new row here, you are offered two options in the data exchange mode. Select the DX mode for direct data exchange and specify the parameters.

Fig. 4: Configuration of the CPU 315-2DP with DP address 4

  1. This enables the second DP slave to "listen in" on the data that the first DP slave sends to the DP master.

In the following is a sample project - created in STEP 7 V5.2 SP1 - for internode communication (German = Querverkehr) between two CPUs. Proceed as follows:

  1. Save "QuerVerkehr.exe" in an empty directory.
  2. Double-click this file to unpack the project.
  3. Start the SIMATIC Manager.
  4. Open the project.

 QuerVerkehr.exe ( 448 KB )  

A CPU 318 is used as master in the sample project. An active communication is is set up between the master and a CPU 315 as slave. The second CPU 315 "listens in" on this data communication and can respond to events directly. It is not necessary for the master to trigger these events.

Requirements for using internode communication:

  • The master CPU and both DP slaves must be integrated in one STEP 7 project.
  • All stations involved in the internode communication must support "Send and receive capability for direct data exchange".

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