Siemens Simatic S7-300 CP 341 - Handling Erroneous Data; Figure 2-7 Data Traffic When Erroneous Data Is Received

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
44 Manual, 09/2008, A5E02191071-01
2.4.6 Handling Erroneous Data
Handling erroneous data
The figure below illustrates how erroneous data is handled with the 3964(R) procedure.
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Figure 2-7 Data traffic when erroneous data is received
After receipt of DLE, ETX, BCC, the CP 341 compares the BCC of the communication
partner with its own internally calculated value. If the BCC is correct and no other receive
errors occur, the CP 341 responds with DLE.
Otherwise, the CP 341 responds with an NAK and waits the block wait time (T) of 4 seconds
for a new attempt. If after the assigned number of transmission attempts the block cannot be
received, or if no further attempt is made within the block wait time, the CP 341 cancels the
receive operation.
Extended error display at the receive FB
Activate the parameter "Display receive error at FB" to also display a message frame
received with errors at the status output of the function block P_RCV_RK.
If the parameter is deactivated, an entry is only created in the diagnostic buffer of the
CP 341.
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