Figure 2-9 Flow Diagram Of The Start-Up Of The 3964(R) Procedure - Siemens Simatic S7-300 CP 341 User Manual

Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
Procedure errors
The procedure recognizes both errors caused by faulty communication partner behavior and
errors caused by faults on the line.
In both cases, the procedure initially attempts to send/receive the data block correctly. If the
data block cannot be sent or received error-free within the maximum specified number of
transmission attempts (or if a new error status occurs), the procedure cancels the send or
receive operation. It reports the error number of the first error detected and returns to the idle
state. These error messages are displayed in the STATUS output of the FB.
If the system program frequently reports an error number at the STATUS output of the FB for
send and receive repetitions, this implies occasional disturbances in data traffic. The high
number of transmission attempts balances this out, however. In this case, you are advised to
check the transmission link for possible sources of interference, because frequent repetitions
reduce the user-data rate and integrity of the transmission. However, the disturbance could
also be the result of a malfunction on the part of the communication partner.
In the event of a BREAK on the receive line (receive line interrupted), an error message is
indicated at the STATUS output of the FB. No repetition is started. The BREAK status is
automatically reset as soon as the connection is restored on the line.
For every detected transmission error (lost character, frame or parity error), a standard
number is reported, regardless of whether the error was detected during sending or receiving
of a data block. The error is only reported, however, if previous repetition attempts have
failed.
3964(R) procedure startup
The figure below illustrates the start-up of the 3964(R) procedure.
Figure 2-9
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Flow diagram of the start-up of the 3964(R) Procedure
CP 341 Point-to-Point Communication, Installation and Parameter Assignment
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Manual, 09/2008, A5E02191071-01