Beckhoff CX8110, Manual, Page: 55 / 73

Programming
CX8110 55 Version: 1.4
Real-time clock (RTC) running too slow
TwinCAT uses its own real-time driver. This has the advantage that the quality of the real-time has been
much improved, and the jitter of the task has been reduced to a minimum. This calls the operating system
from TwinCAT. The RTC on the operating system is controlled via TwinCAT and must be called at certain
times.
If the task cycle time on the TwinCAT side is very long and the CPU load is high, the operating system is no
longer called with sufficient frequency. As a result, the RTC on the operating system is slow. If you have
noticed that the RTC is slow and the time on the CX8110 is also slow, you can apply the following
troubleshooting procedure.
Remedy
The call of the RTC is always linked to a reading of the hardware RTC. This has the disadvantage of a
slightly higher CPU load, but since the CPU load is already high due to your application, the additional CPU
load is negligible. Adjust the settings in the registry:
[HKEY_LOCAL_MACHINE\Platform]
“SoftRTC"=dword:0
Table 15: Description of the SoftRTC registry key
Value Description
0 The hardware RTC is always read out when the Windows time is
requested.
1 The hardware RTC is read out once at startup. From then on, the
Windows clock continues to run via the internal system tick.
Standard setting: "SoftRTC"=dword:1