Watchdog; Buffering - Siemens SIMATIC FM 456-2 Installation, Hardware, And Startup

4.8

Watchdog

Method of Operation
The FM 456-2 contains a watchdog for monitoring user programs. This is called on
a cyclic basis by the system software. If the cyclic operation fails (for instance, if
the software "hangs"), the module is reset after the watchdog period has expired.
The cause of the reset is stored and is evaluated by the diagnosis software.
4.9

Buffering

The S7-400 rack is buffered centrally by the back-up battery in the power supply
module.
If central buffering is present, the time and date and the SRAM (256 Kbytes) is
buffered on the FM 456-2 application function module.
Note
Note that the data content will be lost if the central buffering fails or the module is
unplugged from the rack.
BIOS Setup
The BIOS setup data, excluding time and date, is stored in the BIOS flash EPROM
and is therefore independent of the central buffering. The BIOS setup is retained if
the central buffering fails or the FM 456-2 is removed from the rack.
FM 456-2 Application Function Module Installation, Hardware, and Startup
C79000-G7076-C458-01
FM 456-2 Functions and Technical Data
4-11