Security Measures - DZG DVS74 Series Product Manual

product manual DVS74
The functionality of the meter is periodically processed in the main loop of the application layer. The
main loop is interupted by interrupt service routines based on timer events and asynchron events.
Figure 14Firmware flow diagram

12.3 Security measures

Measures against unintentional or intentional changes of the firmware:
MCU runs system self check to monitor the internal flash for firmware storage to avoid the changes
for firmware. Parts of flash area are fixed with constant value. This value will be checked periodically.
Measures in case of a crash of the firmware (Fault recovery, Wactdog,...).
System has internal watchdog. Firmware will kick-off watchdog within 1.25s. If it is not executed
correctly, the whole system will be reset.
Measures for secure memory of the energy registers (back up facilities,...).
There is backup data for energy register and calibration data. When these data are produced, the
current data and backup data will be stored together in different areas. For these important data, each
parameter has a checksum. Firmware will validate the data by check sum. If there is error, the backup
data will be recovered for use.
Measures against unintended or intended reset of the energy registers
Firmware does not provide the interface to reset the energy registers. If there was situation which lead
to current energy registers reset the firmware will recognize it by check sum validation, then the back
up data will be used.
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22.02.2019 Page 32 / 38