GE PACSystems RX7i, User Manual

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Chapter 5. Ethernet Global Data
84 PACSystems* RX7i & RX3i TCP/IP Ethernet Communications User Manual GFK-2224Q
Clock Status and Stratum Format
Clock Status and Stratum PLC memory address Clock Status
Clock Status and Stratum PLC memory a 1 Clock Stratum
An Ethernet Interface can maintain timing information from up to four SNTP servers at a time. Each server
assigns a stratum number that determines its priority.
When locked to a network timeserver, the Ethernet clock stratum value indicates the accuracy of the time
value provided by the server. A stratum value of 1 indicates the highest accuracy time; a value of 15 indicates
the lowest accuracy. A stratum value of 255 indicates that the Ethernet clock is not locked to any timeserver.
Before using this stratum value, always check that the corresponding clock status indicates that the Ethernet
clock is locked to a network timeserver.
The
Status word indicates whether the Ethernet clock is locked to a network timeserver.
Clock Status Word Values
Value Description
0 Ethernet interface is not configured for SNTP operation
1 Ethernet clock is currently locked to network timer server
2 Ethernet clock is not locked to network timer server
Note: Bit 5 in the LAN Interface Status (LIS) block indicates whether the Ethernet module is currently locked to
an SNTP timeserver on the network. The logic application can periodically examine this bit to
determine when an Ethernet module has lost its lock with a network timeserver. For details of the LIS
block, refer to “Monitoring the Ethernet Interface Status Bits” in Chapter 12.
Enable or Disable PLC Time Update COMMREQ (5002)
This COMMREQ is used to enable or disable a specific Ethernet interface to update the CPU’s TOD clock. When
enabled, the Ethernet interface updates the TOD clock each time that a time update message is received from
an SNTP server on the network. If the Ethernet interface is locked to a timer server when this COMMREQ
command is issued, the Ethernet interface immediately updates the TOD clock with the current synchronized
clock value.