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Entry type: FAQ, Entry ID: 27073039, Entry date: 02/14/2011

What properties, advantages and special features does the procedure 3964 (R) offer?

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The procedure 3964 (R) protocol controls data transfer via point-to-point connection between a local station and a communication partner. The procedure 3964 (R) includes the bit transfer layer (layer 1 of the ISO-OSI reference model) and the security layer (layer 2).
This security layer is available in the form of a control character. This control character checks the complete and error-free data transfer from the communication partner.
In the case of a connection via the procedure 3964 (R), the two communication partners must be configured with different priorities.

Protocol services:

Service Description
SEND The SEND function available for the system concerned in each case transfers a data area from a data block. This data area is defined by the data block number, the initial address and the length of the data to be transferred.
RECEIVE The RECEIVE function available for the system concerned in each case transfers received data areas from a data puffer into a target area. The target area is specified in the local station by a data block and the initial address of the data. The length of the data received is output after successful completion of the function.

Advantages of the protocol:

  • Can be used well with third-party systems.
  • Suitable only for medium data volumes (<= 4096 bytes)
  • Data transfer acknowledged by the communication partner
  • High data security (hamming distance 3)

Disadvantages of the protocol:

  • RS 485 cannot be used as bus medium
  • Requires coordinated calls of send and receive functions

Quantity framework:

Parameters Value range
Data area per job Up to 4096 bytes per message
Logical interface Layer 2 of the ISO-OSI reference model
Number of possible connections per CP 1 per interface (point-to-point)


  • General information on communication via SIMATIC S7 and a detailed description of the procedure 3964 (R) are available in Entry ID: 20982954.
  • The difference between procedure 3964 and procedure 3964 (R) lies in the transfer of block check characters. Block check characters are transferred in procedure 3964 (R)

RK 512, Point-to-point, Serial connection, Third-party system

Security information
In order to protect plants, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art industrial security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about industrial security, please visit