Time-Of-Day Synchronization" Parameter Group - Mode - Siemens S7-300 Configuration Manual

Configuring the Ethernet CP with STEP 7
3.3 Setting further CP properties
3.3.5

"Time-of-day synchronization" parameter group - mode

Method for time-of-day synchronization
The CP provides the following methods for time-of-day synchronization and these are
described below:
● SIMATIC mode
● NTP mode (NTP: Network Time Protocol)
How it works
● SIMATIC mode
When the CP receives MMS time messages, its local time is synchronized provided that
the NTP mode was not configured (MMS = Manufacturing Message Specification).
The advantage of this mode is that it is generally more accurate than the NTP mode.
The time messages are received either from an S7-41x CPU or from the LAN.
located:
– Case a) Time messages come from the subnet (LAN) and are forwarded to the
– Case b) Time messages come from the station and are forwarded to the subnet
If you have several CPs in your station, take into account the flow of time-of-day
messages depending on the time-of-day master. It is possible to transfer time-of-day
messages from one network to another network using the function described here. There
may, however, only be one time master in your station.
If there are several CPs that are connected to the same network in a station, only one of
these CPs may forward the time messages.
Note
During configuration, there is no consistency check relating to this option when
configuring several CPs.
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You can choose whether or not the CP simply adopts the time or also forwards it. If a
different instance is set up to forward the time, do not select forwarding.
The two following situations are possible depending on where the time-of-day master is
station. In this case, the CPU's time synchronization must be configured as a slave.
(LAN). In this case, a time-of-day synchronization of the CPU must be configured as
the master or another CP forwards time messages to the K bus.
Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13