Clock Synchronization Of Multiple Relays - GE Feeder Management Relay 750 Instruction Manual

7.3 MODBUS OPERATIONS
Table 7–3: EXCEPTION RESPONSE ERROR CODES
ERROR MODBUS DEFINITION
CODE
01 ILLEGAL FUNCTION
02 ILLEGAL DATA ADDRESS
03 ILLEGAL DATA VALUE
04 FAILURE IN ASSOCIATED
DEVICE
05* ACKNOWLEDGE
06* BUSY, REJECTED MESSAGE
07* NAK - NEGATIVE
ACKNOWLEDGE
* Some Modbus implementations may not support these exception responses
The time and date of multiple relays on the same communication link can be synchronized so that time stamping 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 synchro-
nize the dates.
3. Broadcast (via slave address 0) the Set Time operation code via function code 05h to all connected slaves to synchro-
nize 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
7
and time of 2:15:30 PM to slave device 11 as required by step one of the procedure.
MASTER QUERY MESSAGE:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte, low order byte
NUMBER OF SETPOINTS: high order byte, low order byte
BYTE COUNT
DATA #1: high order byte, low order byte
DATA #2: high order byte, low order byte
DATA #3: high order byte, low order byte
DATA #4: high order byte, low order byte
CRC: low order byte, high order byte
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS: high order byte, low order byte
NUMBER OF BYTES: high order byte, low order byte
CRC: low order byte, high order byte
7-8
Courtesy of NationalSwitchgear.com
GE MULTILIN IMPLEMENTATION
The function code of the master query message is not supported by the slave.
The address referenced in the data field of the master query message is not an
address supported by the slave.
The value referenced in the data field of the master query message is not allowable in
the addressed slave location.
An external device connected to the addressed slave device has failed and the data
requested cannot be sent. This response will be returned if a GE Multilin device
connected to the RS485 external device port of the 745 has failed to respond to the
750/760.
The addressed slave device has accepted and is processing a long duration command.
Poll for status.
The message was received without error, but the slave device is engaged in
processing a long duration command. Retransmit later, when the slave device may be
free.
The message was received without error, but the request could not be performed,
because this version of the 750/760 does not have the requested operation available.

7.3.3 CLOCK SYNCHRONIZATION OF MULTIPLE RELAYS

EXAMPLE (HEX):
11 query message for slave 11
10 store multiple setpoint values
10 06 data starting at address 1100h
00 04 4 setpoint values = 8 bytes total
08 8 bytes of data
06 0A Month = 06h (June), Day = 0Ah (10th)
07 CA Year = 07CAh (1994)
0E 0F Time (hour: minute) = 0Eh:0Fh (14:15)
75 30 Time (ms) = 7530h (30000 ms = 30 seconds)
37 0C CRC computed by master
EXAMPLE (HEX):
11 response message from slave 11
10 store multiple setpoint values
10 06 data starting at address 1006h
00 08 4 setpoint values = 8 bytes total
27 9B CRC computed by slave
750/760 Feeder Management Relay
7 COMMUNICATIONS
GE Multilin