Clock Synchronization Of Multiple Relays - GE 750 Manual

CHAPTER 3: MODBUS FUNCTIONS
Table 3: Exception Response Error Codes
Error Modbus Definition
Code
05* Acknowledge
06* Busy, Rejected Message
Nak - Negative
07*
Acknowledge
* Some Modbus implementations may not support these exception responses

Clock Synchronization of Multiple Relays

750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
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.
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 synchronize the dates.
3. Broadcast (via slave address 0) the Set Time operation code via function code 04h 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.
Master Transmission
Slave Address
Function Code
Data Starting Address
Number Of Setpoints
Byte Count
Data #1
Data #2
Data #3
Data #4
CRC (Low, High)
CLOCK SYNCHRONIZATION OF MULTIPLE RELAYS
GE Multilin Implementation
Bytes Example
1 11 message for slave 11
1 10 store multiple setpoints
2 10 06 data at address 1100h
2 00 04 4 setpoints = 8 bytes total
1 08 8 bytes of data
2 06 0A month = 06h (June), day = 0Ah (10)
2 07 CA Year = 07CAh (1994)
2 0E 0F Time (hr:min) = 0Eh:0Fh (14:15)
2 75 30 Time (ms) = 7530h (30000 ms = 30 s)
2 37 0C computed CRC error code
Description
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