1MAC052634-MB D
Section 3
Vendor-specific implementation
615/620 series ANSI
31
Communication Protocol Manual
into the next 11 registers. If this is the first time the client reads events from the IED, the
oldest event of the Modbus event buffer is loaded into the 11 event record registers.
Selection code 2: Reading the oldest stored record
Selection code 2 always forces the event reading to go back to the oldest event in the
Modbus event buffer. The oldest event record is then loaded into the 11 event record
registers. After the client has read out this record, the next record becomes the oldest
unread. The client can continue with the selection code 1 by reading out the oldest unread
event record again.
Selection code -1...-499
A negative selection code, that is a 16 bit two's complement value, defines how many
records backwards from the newest event the event record reading is to be moved. For
example, the ten latest events could be read out at any time by first selecting -10, reading
out the event and then continuing with the selection code 1 to read out the nine additional
event records. There can be 500 event records altogether.
Selection code 3: Resetting the event read pointer
The write selection 3 is not followed by a read operation. The selection 3 means that there
are no unread records in the Modbus event buffer left for the client in question, that is, the
buffer is cleared. The next new event that is logged into the Modbus event buffer becomes
the first unread record for this specific client.
Selection code 4: Resetting SSR3 bit 8
The write selection 4 is not followed by a read operation. The selection code only resets
the bit 8 in SSR3.
3.3.8.3
Other event record registers
Sequence number
Every Modbus event record is given a sequence number. The sequence number runs from
1 to 65535 and then rolls over to 1 again. The client can check that the sequence numbers
of the recorded data are sequential. During the event buffer overflow, the client can notice
a jump in the sequence numbers when some event records are lost. The gap between the
new and the previous sequence number reveals exactly how many event records have been
lost.
If event records are read by using two commands, the client can re-read the
11 event record registers as many times as it wants. As long as no new
selection write operation is performed, the contents of the 11 event record
registers are not changed.
