Clock Synchronization Of Multiple Relays - GE 750 Instruction Manual

16.3 MODBUS PROTOCOL
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
PACKET FORMAT
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS - hi
DATA STARTING ADDRESS - lo
NUMBER OF SETPOINTS - hi
16
NUMBER OF SETPOINTS - lo
BYTE COUNT
DATA #1 - hi (Month = 6)
DATA #1 - lo (Day = 10)
DATA #2 - hi (Year=1994=07CAh)
DATA #2 - lo (Year=1994=07CAh)
DATA #3 - hi (Hour=2pm=14)
DATA #3 - lo (Minute=15)
DATA #4 - hi (Sec=30000ms=7530h)
DATA #4 - lo (Sec=30000ms=7530h)
CRC - lo
CRC - hi
16-
12
Courtesy of NationalSwitchgear.com

16.3.11 CLOCK SYNCHRONIZATION OF MULTIPLE RELAYS

EXAMPLE (HEX)
11
10
10 DATA STARTING ADDRESS - hi
06 DATA STARTING ADDRESS - lo
00 NUMBER OF SETPOINTS - hi
04 NUMBER OF SETPOINTS - lo
08
06
0A
07
CA
0E
0F
75
30
37
0C
750/760 Feeder Management Relay
16 COMMUNICATIONS
SLAVE RESPONSE
PACKET FORMAT
SLAVE ADDRESS
FUNCTION CODE
CRC - lo
CRC - hi
GE Power Management
EXAMPLE (HEX)
11
10
10
06
00
08
27
9B