Siemens SIMATIC S7-1500 System Manual page 220

Compensation for runtime deviations
To compensate for runtime deviations between SIMATIC and SINAMICS clocks, the time is
automatically re-synchronized at regular intervals.
Please note the following response to setting the SINAMICS clock time:
SIMATIC clock time
Great than time/date on SINAMICS
Less than time/date on SINAMICS
This response ensures that the order of SINAMICS diagnostic buffer entries is retained
following runtime difference compensation.
The SINAMICS clock operates with a resolution of 1 ms. A synchronization accuracy of 1 ms
is achieved for all bus clock cycles divisible by 1 ms (for example 1 ms, 2 ms, 3 ms).
For all bus clock cycles that cannot be divided by 1 ms (for example 1.25 ms), a slightly
lower synchronization accuracy is achieved in line with the system.
Precise synchronization is only ensured if OB MC Servo is operated in isochronous mode.
Resetting the time
Parameter p3109 is used to define a threshold that has the following effect in the event of
negative time jumps:
Negative time jump
Less than threshold value
Greater than threshold value
Default setting for the threshold: p3109 = 100 ms
This means that the clock time is reset in the event of negative time jumps of more than
100 ms.
The default value is set so that normal runtime deviations (quartz drift) are below the
threshold. If the CPU clock is set back by more than 100 ms, this is interpreted as an
"intentional clock time reset" and the clock time of the drives is also set back immediately.
The warning A01099 is also output.
If the real-time clock is reset by more than 60 seconds, an entry is also written to the
diagnostic buffer in the drive:
Time correction (adjustment) by <correction value> seconds
Following another synchronization operation (negative time jump greater than the threshold),
the parameter cu.p3107 has the following values:
● p3107[0 ... 1] the UTC time after synchronization
● p3107[2 ... 3] the UTC time before synchronization
[0] and [2] are milliseconds; [1] and [3] are days.
Note
The diagnostic buffer entries are not converted to the new time after the clock time
changeover.
SIMATIC Drive Controller
System Manual, 11/2019, A5E46600094-AA
11.9 Time synchronization
Response of SINAMICS
Time and date are tracked on SINAMICS
The clock on SINAMICS is stopped until the
"Time/date to be set" is reached.
Effect on time
Time is paused (for details, see "Compensation
for runtime deviations")
Clock time is reset
Commissioning
219