QUESTION:
What are the differences between protocols 3964(R) and RK 512 in point-to-point communications?  

ANSWER:
The major differences between to the two protocols are the message header and the response message. Using RK 512 provides the highest data integrity. Below is a reference model with classification of the available protocols:

Fig. 1: Classification of available protocols  

Procedure 3964(R) The procedure 3964(R) adds control characters (security layer) to the information data when transferring it. These control characters enable the communication partner to check whether the data has been received in full and without any errors. The procedures 3964(R) and RK 512 evaluate the following control characters:

Table 1: Overview of control characters

The following figure shows the sequence of data transfer when sending with procedure 3964(R):

Fig. 2: Data traffic when sending with procedure 3964(R)  

Procedure  RK 512 In contrast to procedure 3964(R) the computer link RK 512 has the transport layer (Layer 4) in addition to the bit transfer layer (Layer 1) and the security layer (Layer 2).
The computer link RK 512 also provides higher data integrity and better address options. Fig. 3 shows the sequence of data transfer when sending with a response message using computer link RK 512:

Fig. 3: Data traffic when sending with response message  

More information is available in the electronic manuals listed in Table 2 that you can download from our Web site:

Device	Title	Entry ID
S7-300 / CP 340	Set up and parameterize point-to-point link CP 340	1137332
S7-300 / CP 341	Set up and parameterize point-to-point link CP 341	1117397
S7-400 / CP 440	Set up and parameterize point-to-point link CP 440	2042641
S7-400 / CP 441	Set up and parameterize point-to-point link CP 441	1137419

Table 2: Electronic manuals