Siemens SIMATIC NET CP 243-1 IT Technical Manual page 63

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Activating/deactivating the CRC routine and specifying the monitoring time
After you have finished configuring the S7 connection, you must specify in the next
screen whether your configuration data on the S7-200 CPU are to be protected
with a CRC routine against accidental overwriting.
If the CRC routine is activated, the CP 243-1 IT checks during startup to determine
whether its configuration data which it reads from the memory of the S7-200 CPU
were overwritten from the user program. If so, it terminates startup and attempts to
obtain its TCP/IP address parameters from a BOOTP server. If it succeeds, startup
is continued. However, only the MicroWN channel is activated afterwards. The CP
243-1 IT can then only communicate with STEP 7 Micro/WIN 32 but not with other
controllers.
We recommend always activating the CRC routine. This is the only way in which
the CP 243-1 IT can detect that the user program has made undesired changes to
the configuration data.
If the CRC routine is not activated, your user program can change the configuration
data of the CP 243-1 IT. However, the CP 243-1 IT does not "notice" when this
data is accidentally overwritten.
Caution
An S7-200 user program can only change the configuration data on the S7-200
CPU when the CRC routine is off.
Since, after the CRC routine is disabled, the CP 243-1 IT is no longer able to com-
pletely check the configuration data for consistency concerning desired and unde-
sired changes, there is no guarantee whatsoever that the CP or the components
connected in the network will function correctly.
In the same screen you also can set a common monitoring time (Keep Alive time)
for all configured connections. If a connection partner can suddenly no longer be
accessed (e.g., because the TCP/IP network has malfunctioned or because an er-
ror occurred at the communication partner's), the value entered here determines
the time after which the CP 243-1 IT recognizes this problem.
You already specified which connections are to be monitored with this time when
you configured the individual connections.
CP 243-1 IT
J31069-D0429-U001-A0-7618
Configuration
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