Time-Of-Day Synchronization; Recommendation For Use With A High Communications Load - Siemens SIMATIC NET S7-400 Manual

6.6

Time-of-day synchronization

General rules
On the RNA interface, the CP supports the following two modes for timeofday
synchronization:
● SIMATIC mode
● NTP mode (NTP: Network Time Protocol)
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.
Note
Note the following about timeofday synchronization in NTP mode:
If an NTP frame is detected by the CP as "not exact" (example: NTP server is not
synchronized externally), there is no forwarding on the 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.
Project engineering
For more detailed information on configuration, refer to the online help of the "Time-of-day
synchronization" parameter group and in Part A of the manual /1/ (Page 67).
6.7

Recommendation for use with a high communications load

Reason
To avoid an overload situation on the CPU you are using, note the following information
about the CP.
Known problems
● The program blocks for sending and receiving AG_SEND / AG_RECV (FC5/FC6,
FC50/60 or FC53/63) are often called cyclically in OB1. This leads to constant
communication between the CPU and CP. As a result, other types of communication
such as PG functions cannot be executed or only very slowly.
● HMI systems access data of the CPU too often using S7 functions. This slows down
communication overall and there may be resource bottlenecks on the CPU.
CP 443-1 RNA
Manual, 03/2019, C79000-G8976-C299-04
Configuration and operation
6.6 Time-of-day synchronization
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