Siemens SIMATIC S7-400 CP 440 - Procedure Errors

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
Manual, 09/2007, A5E00057742-03
55
Procedure Errors
The procedure recognizes both errors which are caused by the communication partner and
errors caused by faults on the line.
In both cases, the procedure makes repeated attempts to send/receive the data block
correctly. If this is not possible within the maximum number of transmission attempts set (or
if a new error status occurs), the procedure aborts the send or receive process. It reports the
error number of the first recognized error and returns to idle mode. These error messages
are displayed in the STATUS output of the FB.
If the system program regularly reports an error number at the STATUS output of the FB for
send and receive repetitions, this indicates occasional trouble affecting the data traffic. The
large number of transmission attempts compensates for this, 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. The disturbance could
also be caused, however, by a malfunction on the part of the communication partner.
If BREAK occurs on the receive line (receive line interrupted), an error is displayed at the
STATUS output of the FB. No repeat is started. The BREAK status is automatically reset as
soon as the connection is restored on the line.
For every recognized 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, following unsuccessful repetitions.
3964(R) procedure startup
The figure below illustrates the startup of the 3964(R) procedure.
*
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Figure 2-20 Flow diagram of the startup of the 3964(R) procedure
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