Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
PtP coupling and configuration of CP 340
32 Manual, 04/2011, A5E00369892-03
2.4 Data Transmission with the 3964(R) Procedure
Introduction
The 3964(R) procedure control PtP data exchange between the communications processor
and a communication partner. As well as the physical layer (layer 1), the 3964(R) procedure
also incorporates the data-link layer (layer 2).
2.4.1 Control characters
Introduction
During data transmission, the 3964(R) procedure adds control characters to the user data
(data-link layer). These control characters allow the communication partner to check whether
the data has arrived complete and without errors.
The control characters of the 3964(R) Procedure
The 3964(R) procedure analyzes the following control codes:
● STX Start of Text;
Start of the string to be transmitted
● DLE Data Link Escape;
Data Link Escape
● ETX End of Text;
End of string to be transmitted
● BCC Block Check Character (only with 3964R);
Block Check Character
● NAK Negative Acknowledgement;
Negative Acknowledgement
Note
If DLE is transmitted as an information string, it is sent twice so that it can be
distinguished from the control code DLE during connection setup and release on the send
line (DLE duplication). The receiver then reverses the DLE duplication.
Priority
With the 3964(R) procedure, one communication partner must be assigned a higher priority
and the other partner a lower priority. If both partners try to send at the same time, the
partner with the lower priority will defer its send request.
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