ABB REF 610 Technical Reference Manual page 81

1MRS 755535
Feeder Protection Relay
Technical Reference Manual - ANSI Version
Selection code 2: reading the oldest stored record
By resetting the read pointer using selection code 2, the master can read the oldest
stored event record. After this, the master can continue reading the following records
using selection code 1, irrespective of whether they have been read before.
Note!
Resetting the read pointer will not affect the sequence number of the event record.
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 will be 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 will be created for every instantaneous
target point; see the example below.
Momentary
Change detect
Fig. 4.1.15.2.-1 Change detection bit
If the instantaneous value of an target bit has changed two or more times since the
master last read it, the CD bit will be set to one. When the CD bit has been read, it
will be set to zero.
The instantaneous and the CD bit of a certain target point always occur as a pair in
the Modbus memory map.
REF 610
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