Product Manual WS74
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Copyright
DZG Metering GmbH, Heidelberger Str. 32, D-16515 Oranienburg
Copies only are allowed authorized by DZG
2/22/2019
Page 21 / 37
The functionality of the meter is periodically processed in the main loop of the application layer. The
main loop is interrupted by interrupt service routines based on timer events and asynchrony events.
Figure 11 Firmware flow-diagram
12.4
Energy checksum mechanism
The energy registers are stored once in the internal RAM of the MCU and once in the external
EEPROM. In each memory two backups are available. The contents, original and backup, are stored
together with a checksum.
Before the current energy consumption (
△
E) is accumulated to the energy registers in the RAM or
EEPROM the energy registers are red out and the checksum is controlled. If the check sum is not
correct the backup registers are used.
The current
△
E is accumulated to the energy register and the check sum is calculated new. These
information are stored to the memories. Finally, a new back up of the energy registers and the
checksum is created.
Note:
The firmware version is shown on LCD of the meter and can be read when power on.
12.5
Self-Monitoring
The meter has an internal software watch dog. If the firmware is running abnormally without feeding
the watch dog periodically, the watch dog will reset the main CPU. Watchdog events lead to fatal error
if the events occur more times within a defined time slot.
The meter has implemented a self-monitoring system. If the meter recognizes no proper operation
(measurement, memory check, watchdog events) so that billing relevant values may not be used
anymore it displays a „ Fatal Error“.
