GE 750 - Clock Synchronization of Multiple Relays

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750/760 Feeder Management Relay GE Power Management
16.3 MODBUS PROTOCOL 16 COMMUNICATIONS
16
16.3.11 CLOCK SYNCHRONIZATION OF MULTIPLE RELAYS
The time and date of multiple relays on the same communication link can be synchronized so that time stamp-
ing of events on different relays can be correlated. The following procedure describes how to synchronize the
clocks of multiple relays. Since the clock is accurate to 1 minute per month, performing this procedure every 10
minutes will result in synchronization accuracy of ±10 ms.
1. Store values for the date and time setpoints Set Date and Set Time at locations 1006h and 1008h in the
Memory Map respectively into each slave device.
2. Broadcast (via slave address 0) the SET DATE operation code via function code 05h to all connected
slaves to synchronize the dates.
3. Broadcast (via slave address 0) the SET TIME operation code via function code 05h to all connected
slaves to synchronize the times. If synchronizing to an external clock source then this command should be
sent when the time is equal to the value stored in SET TIME.
The following table shows the format of the master and slave packets for a master device storing the date of
June 10, 1994 and time of 2:15:30 PM to slave device 11 as required by step one of the procedure.
Table 16–10: MASTER/SLAVE PACKET FORMAT FOR CLOCK SYNCHRONIZATION
MASTER TRANSMISSION SLAVE RESPONSE
PACKET FORMAT EXAMPLE (HEX) PACKET FORMAT EXAMPLE (HEX)
SLAVE ADDRESS 11 SLAVE ADDRESS 11
FUNCTION CODE 10 FUNCTION CODE 10
DATA STARTING ADDRESS - hi 10 DATA STARTING ADDRESS - hi 10
DATA STARTING ADDRESS - lo 06 DATA STARTING ADDRESS - lo 06
NUMBER OF SETPOINTS - hi 00 NUMBER OF SETPOINTS - hi 00
NUMBER OF SETPOINTS - lo 04 NUMBER OF SETPOINTS - lo 08
BYTE COUNT 08 CRC - lo 27
DATA #1 - hi (Month = 6) 06 CRC - hi 9B
DATA #1 - lo (Day = 10) 0A
DATA #2 - hi (Year=1994=07CAh) 07
DATA #2 - lo (Year=1994=07CAh) CA
DATA #3 - hi (Hour=2pm=14) 0E
DATA #3 - lo (Minute=15) 0F
DATA #4 - hi (Sec=30000ms=7530h) 75
DATA #4 - lo (Sec=30000ms=7530h) 30
CRC - lo 37
CRC - hi 0C