GE PACSystems RX7i, User Manual

Page: 92 / 276

Chapter 5. Ethernet Global Data
GFK-2224Q January 2017 79
CPU Ethernet
interface
SNTP Time
CPU
time
clock
SNTP Time
Server on
Network
timestamp
EGD with
timestamp
time
clock
Figure 42: Obtaining Timestamps from the SNTP Server’s Time Clock
Obtaining Timestamps from the CPU TOD Clock
Synchronizing the CPU TOD clock to an SNTP server allows you to set a consistent time across multiple systems.
Once the CPU TOD clock is synchronized with the SNTP time, all produced EGD exchanges will use the CPU’s
TOD for the time stamp.
Synchronizing the CPU TOD clock to a network timeserver requires CPU firmware version 5.00 or greater. Each
participating Ethernet interface must use firmware version 5.00 or greater. Older firmware versions do not
support the necessary COMMREQ commands.
Synchronizing the CPU TOD Clock to an SNTP Server
The CPU TOD clock is set with accuracy within ±2ms of the SNTP time stamp.
CPU TOD clock synchronization is enabled on an Ethernet module by setting the Advanced User Parameter
(AUP) ncpu_sync to 1. For details on configuring an AUP file, refer to Appendix A.
Note that CPU TOD clock synchronization is enabled automatically when SNTP is enabled within PME for a
CPE305, CPE310, CPE330 and CPE400.
Within a PLC, only one Ethernet interface at a time can be selected as the time master for CPU time
synchronization. If multiple Ethernet modules are configured for CPU time synchronization, the PLC application
logic should issue a
Read Ethernet Clock Status and Stratum COMMREQ (5001)
to each configured module. The
application logic must examine the stratum number at each Ethernet module to determine which Ethernet
module to select. When the application has determined which module to use as the time master, it must send
an
Enable PLC Time Update COMMREQ (5002)
to that module.
When the CPU TOD is used for EGD time stamps, it continues until a STOP transition occurs. On a RUN to STOP
transition, the CPU disables CPU TOD clock synchronization. The PLC application logic must enable CPU TOD
clock synchronization by sending an Enable PLC Time Update COMMREQ (5002) on every STOP to RUN
transition.
For an overview of this operating sequence, see page 81.
Note: With the AUP parameter ncpu_sync =1, the Ethernet modules get their time from the
SNTP network server regardless of the Network Time Sync setting in the Ethernet
module’s hardware configuration.