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REF 610
80
Feeder Protection Relay
Technical Reference Manual
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) indication bit will be created for every momentary
indication point; see the example below.
Momentary
Change detect
Fig. 4.1.15.2.-1 Change detection bit
If the momentary value of an indication 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 momentary and the CD bit of a certain indication point always occur as a pair
in the Modbus memory map.
Modbus data mapping
There are two types of monitoring data: digital indications and measurands. For
convenience and efficiency, the same data can be read from different data areas.
Measurands and other 16-bit values can be read either from the IR or HR
1MRS 755310
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