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If the CP receives time-of-day frames at intervals of 1 second, the CP still only synchronizes
the time on the CPU once every minute. This means that the time value on the CPU jumps
less often.
8.6
Time-of-day synchronization
General rules
The CP supports the two modes explained below for time-of-day synchronization:
● SIMATIC mode
● NTP mode (NTP: Network Time Protocol)
Forwarding the time-of-day message
You can configure the direction in which time-of-day messages are forwarded in STEP 7 /
NCM S7 in the properties dialog of the CP as follows:
● Configuration "from station to LAN"
● Configuration "from LAN to station"
CP 343-1 ERPC
Manual, 03/2010, C79000-G8976-C239-02
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-of-day synchronization in NTP mode:
If an NTP frame is detected by the CP as "not exact" (example: NTP server is not
synchronized externally), the CP does not synchronize itself and does not forward the
time on the communication bus (K 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.
The CP forwards time frames from the CPU to Industrial Ethernet when the local CPU is
time master (SIMATIC mode only) or when the time of day is forwarded by a different CP
on the K bus.
The CP forwards time frames from Industrial Ethernet to the CPU when one of the
following components is time master:
In SIMATIC mode:
– a remote CPU 41x
– a remote CPU 31x
– a SIMATIC NET time transmitter
– a CP 1430 TF
an NTP server when using NTP mode
Further notes on operation
8.6 Time-of-day synchronization
61
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