Siemens SIMATIC CP 340 User Manual page 45

Procedure errors
The procedure recognizes both errors 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 repeat 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 error detected and returns to 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
repetition frequency 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. The disturbance could also be caused,
however, by a malfunction on the part of the communication partner.
If the receive line is interrupted, the system program reports a BREAK status (a break is
displayed via the diagnostic interrupt on the CP 340) (see Chapter "Diagnostics via the S7-
300 backplane bus (Page 142)"). No repetition is started. The BREAK status in the STATUS
output of the FB is automatically reset as soon as the connection is restored on the line. A
BREAK evaluation occurs only if BREAK monitoring is not deactivated with the parameter
assignment user interface.
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, following unsuccessful repetitions.
PtP coupling and configuration of CP 340
Manual, 04/2011, A5E00369892-03
Basic Principles of Serial Data Transmission
2.4 Data Transmission with the 3964(R) Procedure
45