7 Time Synchronization
7.4 External Time Synchronization via Fieldbus
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SICAM I/O Unit, 7XV5673, Device Manual
E50417-H1040-C484-A3, Edition 05.2012
Switching Back from the Secondary to the Primary NTP Server
While the device is synchronized by the secondary NTP server, it continues to cyclically poll the primary NTP
server. The device will only switch back to the primary NTP server if it receives correct time information and if
none of the criteria for
are fulfilled anymore.
7.4
External Time Synchronization via Fieldbus
If the device is connected with systems control via the serial FO or the RS485 interface through the
Modbus RTU
protocol, then the external time synchronization is used via fieldbus.
The time information can also be transmitted from the systems control via
Modbus TCP
or
Modbus UDP
using
Ethernet. When using the Ethernet connection, we recommend, however, to synchronize the device from an
NTP server, see chapter 7.3.
For external time synchronization via fieldbus, a telegram is sent cyclically from the client to the device every
minute, together with the time information.
The time synchronization error using the
Modbus RTU
protocol is ±20 ms max.
7.5
Internal Time Synchronization via RTC
Besides external time synchronization, the internal time synchronization is also possible using the battery-
buffered RTC. The SICAM I/O Unit features a quartz oscillator for this purpose.
The time offset of internal time synchronization is 86 ms/day maximum. Due to the reduced accuracy, RTC
should only be used in case of failure or unavailability of the external time synchronization.
NOTE
The parameterization of time is described in detail in chapter 6.3.3.5, section Time Synchronization via Ether-
net NTP. For information regarding the data format, refer to chapter 8.2.7.1 and chapter 8.2.8.4.
NOTE
The parameterization of time is described in detail in chapter 6.3.3.5, section Time Synchronization via Field-
bus (Modbus). For information regarding the data format, refer to chapter 8.2.7.1 and chapter 8.2.8.4.
NOTE
The parameterization of time is described in detail in chapter 6.3.3.5, section Internal Time Synchronization.
For information regarding the data format, refer to chapter 8.2.7.1 and chapter 8.2.8.4.
MAN_SICAM_IO-Unit_7XV5673_US.book Page 132 Thursday, May 10, 2012 10:59 AM