10 Further Notes on Operation
B4A
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64
CP 443-1 Advanced for Industrial Ethernet / Manual Part B4A
Release 01/2007
C79000-G8976-C193-06
10.3
Time-of-Day Synchronization
Procedure
The CP supports the two modes explained below for time-of-day synchronization:
S
SIMATIC mode
If the CP receives MMS time-of-day messages, its local time is synchronized
providing the NTP mode was not defined during configuration (MMS =
Manufacturing Message Specification).
The advantage of this mode is that it is generally more accurate than the NTP
mode (guar
−
1ms). In contrast to the NTP mode, it is not possible to
forward the time of day over routers; in other words, to other subnets.
S
NTP mode (NTP: Network Time Protocol)
In the NTP mode, the CP sends time queries (in the client mode) at regular
intervals to the NTP server in the subnet (LAN). Based on the responses of the
server, the most reliable and most accurate time of day is calculated and the
time synchronized on the station (in all modules with time
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of
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day functionality).
The advantage of this mode is that time-of-day synchronization is possible over
different subnets. The accuracy depends on the quality of the NTP server used.
Note
No automatic changeover to daylight saving is defined in NTP. As a result, you
may need to implement this changeover using a program application.
Notice
Note the following regarding time
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of
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day synchronization in NTP mode:
If the CP recognizes an NTP frame as being “not exact” (example: NTP server is
not externally synchronized), it is not forwarded to the communication bus. If this
problem occurs, none of the NTP servers is displayed as “NTP master” in the
diagnostics; rather all NTP servers are displayed only as being accessible.