The Control Characters
The 3964(R) procedure analyzes the following control codes:
• STXStart of Text;
start of character string for transfer
• DLEData Link Escape;
data connection escape
• ETXEnd of Text;
end of character string for transfer
• BCCBlock Check Character (3964R only)
• NAKNegative Acknowledge
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 begin connection setup at the same time, the
partner with the lower priority will defer its send request.
Basic Principles of Serial Data Transmission
2.5 Data Transmission with the 3964(R) Procedure
Point-to-point connection CP 440 Installation and Parameter Assignment
36 Equipment Manual, 03/2022, A5E00057742-AE
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