Siemens SIMATIC NET TeleControl S7-1200 CP 1243-1 Operating Instructions Manual page 52

Configuration
4.8 Security
Time-of-day synchronization of the CPU
As the synchronization method, with the CPU only NTP can be selected.
If for the CPU the option "CPU synchronizes the modules of the device" is enabled, all smart
modules of the station (CPs as of firmware V2.1.7) are synchronized with the CPU time in a
synchronization cycle of 10 seconds.
Note
Recommendation: Time-of-day synchronization only by 1 module
Only have the time of day of the station from an external time source synchronized by a
single module so that a consistent time of day is maintained within the station.
When the CPU takes the time from the CP, disable time-of-day synchronization of the CPU.
Forwarding the time from the CP to the CPU
Note
Forwarding the time to the CPU
Depending on the firmware version of the modules involved, the time-of-day of the CP is
forwarded to the CPU in different ways:
• Optional forwarding of the CP time to the CPU using a PLC tag
• Obligatory forwarding of the CP time to the CPU via the backplane bus
The forwarding of the CP time to the CPU depends on the firmware version of the CP and
the CPU. Note the following behaviour.
● CP firmware ≤ V2.1.6
With this firmware version the CP can make the time-of-day available to the CPU as an
option via a PLC tag. When this PLC tag is read cyclically by the CPU, the CPU adopts
the CP time.
In the parameter group "Communication with the CPU", you can set whether or not the
current time of day of the CP will be made available to the CPU via a PLC tag. For TLC
tags, see parameter group "Communication with the CPU" of the CP.
● CP firmware ≥ V2.1.7 and CPU firmware ≥ V4.2
If both modules in the station have one of the named firmware versions, the time of day of
the CP is automatically forwarded to the CPU. Since the CPU automatically adopts the
CP time, you no longer require the forwarding option using the PLC tag.
If for the CPU the option "CPU synchronizes the modules of the device" is enabled in
"PROFINET interface > Time synchronization", all smart modules of the station are
synchronized with the CPU time.
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Operating Instructions, 12/2016, C79000-G8976-C365-02
CP 1243-1