
750/760 FEEDER MANAGEMENT RELAY – COMMUNICATIONS GUIDE
4 - 1
750/760 Feeder Management Relay
Chapter 4: Modbus Memory Map
GE
Grid Solutions
Modbus Memory Map
Reading the Event Recorder
All Event Recorder data can be read from Modbus registers found in the address range
2000h to 20FFh.
The ‘Number of Events Since Last Clear’ register at address 2001h is incremented by one
every time a new event occurs. The register is cleared to zero when the Event Recorder is
cleared. When a new event occurs, it is assigned an ‘event number’ which is equal to the
incremented value of this register; the newest event will have an event number equal to
the Number of Events. This register can be used to determine if any new events have
occurred by periodically reading the register to see if the value has changed. If the Number
of Events has increased then there are new events available.
Only the data for a single event can be read from the Modbus memory map in a single
data packet. The ‘Event Number Selector’ register at address 2000h selects the event
number for which data can be read from the memory map. For example, to read the data
for event number 123, the value 123 must first be written to this register. All the data for
event number 123 can now be read from the ‘Event Record Data’ registers at addresses
2010h to 2029h. Only the last 128 events are actually stored in the relay’s memory.
Attempting to retrieve data for elder events that are not stored will result in a Modbus
exception response when writing to the ‘Event Number Selector’.
The following example illustrates how information can be retrieved from the Event
Recorder:
A SCADA system polls the Number of Events register once every minute. It now reads a
value of 27 from the register when previously the value was 24 which means that three
new events have occurred. The SCADA system writes a value of 25 to the Event Number
Selector register. It then reads the data for event number 25 from the Event Record Data
registers and stores the data to permanent memory for retrieval by an operator. The
system now writes the value 26 to the selector and then reads the data for event number