ABB RELION REF610, Technical Reference Manual

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Selection code -1...-99
With selection code -1...-99, the master can move backwards from the newest event
as many events as defined by the selection code and read that specific event record.
After this, the master can continue reading the following records using selection
code 1, irrespective of whether they have been read before.
*
Special case: If there is not as many events in the buffer as specified by the
selection code, the oldest stored event is read.
Selection code 3
The Modbus event buffer is cleared with selection code 3. Clearing the buffer does
not require any read operation to follow.
Digital inputs
As the master may not detect the state changes of all digital signals when scanning,
an additional change detect (CD) target bit is created for every instantaneous target
point; see the example below.
Momentary
Master reads Master reads Master reads Master reads
Change detect
A040332
Fig. 5.1.15.1.-1 Change detection bit
If the instantaneous value of a target bit has changed two or more times since the
master last read it, the CD bit is set to one. When the CD bit has been read, it is set
to zero.
The instantaneous and the CD bit of a certain target point always occur as a pair in
the Modbus memory map.
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REF610 REF610 Feeder Protection Relay
Technical Reference Manual - ANSI Version
1MRS755535