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Entry type: FAQ Entry ID: 13031042, Entry date: 10/02/2002
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Point-to-Point-Interconnection S7-400 / CP 441 

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QUESTION: 
What has to be considered for a point-to-point interconnection with S7-400 / CP 441?

ANSWER:  
The CP 441 supports the protocols 3964(R), data processor RK 512 ( only CP 441-2), ASCIIdriver and printer driver. The use of the data processor RK 512 should be used preferentially. That assures a high transmission security on the transmission line. 

With CP 441-2 at a PzP-Interconnection with RK 512 it is possible to differentiate between passive and active communication.

1. Passive communication
With this transmission you do not have to carry out any progamming in the user program of the passive communication partner.

In order to send data you can use the system function block "BSEND" (SFB 12) or "PUT" (SFB 15) . With this block a dynamically alterable target is possible. In order to read data of a communication partner you have to use the system function block "GET" (SFB 14).

With this communication you have to consider the fact that the passive communication partner cannot recognize when the data transfer takes place. The active partner is also unable to protect the data range needed for the communication against the write access of the passive partner. The passive communication partner at any time has the possibility to overwrite the data while they are being transferred. With the passive communication a consistent data tranfer is notensured.

In the following figure you can see the passive communication through RK 512.

Picture 1: Passive Communication ( 7 KB )  

2. Active Communication
On the transmitter as well as on the receiver side the according programm blocks have to be provided.

With this communication you have the possibility to carry out an analysis on the transmitter side to assure that the communication is finished and that the communication partner received all the data sent. Thus you prevent an overwriting and the data can be transferred consitently.

The following picture demonstrates the active communication through RK 512.

Figure 2: Active Communication  ( 4 KB )  

For further information see chapter 5 and 6 in the manual "Point-to-Point-Interconnection CP 441 Structure and Parameter". The manual you will find under Enty-ID 1137419.

Keywords:
serial transmission mode system, communication planning


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