Security; Configuration - Siemens SIMATIC NET CP 243-1 IT Technical Manual

03/03
2.6

Security

2.6.1

Configuration

Part of the configuration of the CP 243-1 IT is retentively stored on the S7-200
CPU and part in the file system of the CP 243-1 IT. The validity of the portion of the
configuration stored on the S7-200 CPU is secured by a CRC routine. In contrast,
no CRC routine is used for the portion of the configuration stored in the file system
of the CP 243-1 IT.
While storing a configuration on the CP 243-1 IT, STEP 7 Micro/WIN 32 calculates
a CRC checksum. This checksum is stored together with one part of the configura-
tion. While reading out the portion of its configuration stored on the S7-200 CPU,
the CP 243-1 IT checks this checksum so that it can detect undesired changes in
the stored configuration data.
This CRC routine can also be deactivated, however. The configuration can then be
changed manually or by an S7-200 user program.
Caution
Since, after the CRC check is disabled, the CP 243-1 IT is no longer able to check
the configuration data for consistency concerning desired or undesired changes,
there is no guarantee whatsoever that the CP or the components connected to the
network will function correctly.
Caution
The CP 243-1 IT recognizes that the CRC is disabled by a special value of a byte
in its configuration. If precisely this value is set in the configuration either coinci-
dentally or intentionally, this may disable the CRC test. This is why we strongly
recommend only creating the configuration with the Internet wizard integrated in
STEP 7 Micro/WIN 32 and checking the S7-200 program for memory operations
which affect in the data area in which the configuration data of the CP 243-1 IT are
stored.
CP 243-1 IT
J31069-D0429-U001-A0-7618
Features and Functions
41