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The specifications for the communications end points ("TSAPs") in STEP 7 and in
Enabling / disabling the CRC mechanism and defining the Keep Alive time
Once you have configured the connections, you must specify in the next dialog
whether or not your configuration data on the S7-200 CPU are to be protected by a
CRC mechanism against being unintentionally overwritten.
If the CRC mechanism is enabled, the CP 243-1 checks, while it is booting,
whether its configuration data, which it reads out of the memory of the S7-200
CPU, were overwritten by the user program. If so, it stops booting and attempts to
retrieve its TCP/IP address parameters from a BOOTP server. If successful, it continues
booting. In this case, however, only the MicroWN channel is enabled. Thus,
the CP 243-1 can then only communicate with STEP 7 Micro/WIN 32 but not with
other communication partners.
Activating the CRC mechanism is recommended. This is the only way that the
CP 243-1 can recognize unintended changes to the configuration data by the user
program.
If the CRC mechanism is not enabled, you can change the configuration data of
the CP 243-1 in the user program. However, the CP 243-1 will not be able to recognize
if the data have been unintentionally overwritten.
Attention
An S7-200 user program can only be used to configure data if the CRC mechanism
has been switched off.
The CP 243-1 cannot completely check the configuration data for consistency with
regard to intentional and unintentional changes after the CRC check has been
switched off. Therefore, in this case there is no guarantee whatsoever that the CP
or the components connected in the network will function correctly.
In the same dialog you also can set a common monitoring time (Keep Alive time)
for all configured connections. The value entered here determines the time after
which the CP 243-1 IT recognizes the communication problem described in chapter
2.3.3
You have already specified which connections are to be monitored with this time
when you configured the inpidual connections.
Defining the memory area for storing the configuration
Finally, use the next dialog to define the memory area in which your configuration
data is to be stored on the S7-200 CPU. The Wizard will assist you in doing so.
The Wizard then informs you about which subroutines it is establishing on the basis
of your configuration and where your configuration data is being stored.
Configuration of the system is now complete.
Attention
Ensure that the memory area in which the Ethernet Wizard stores the configuration
data is not used by your S7-200 user program.
4.4 Configuring a CP 243-1 from a user program
The configuration data of the CP 243-1 is stored in the S7-200 CPU memory and
can therefore be changed directly from an S7-200 user program. The cyclic redundancy
check (CRC) must be disabled for the configuration data so that the
CP 243-1 will accept configuration data which was changed in this way during the
next startup. For this purpose, the value 16#AC must be entered for Byte 13 of the
CDB data structure. This takes place automatically as soon as the CRC mechanism
is switched off in the Ethernet Wizard.
Attention
Configuring the CP 243-1 from a user program is only recommended for experienced
programmers.
The CP 243-1 cannot completely check the configuration data for consistency with
regard to intentional and unintentional changes after the CRC check has been
switched off. Therefore, in this case there is no guarantee whatsoever that the CP