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1MRS 755310
Feeder Protection Relay
Technical Reference Manual
Special case 2: If the master tries to read the next unread fault record without
entering selection code 1 again, the contents of the last read record will be returned.
Selection code 2: The master reads the oldest stored record
By resetting the read pointer using selection code 2, the master can read the oldest
stored fault 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 fault record.
Note!
A master reset, i.e. clearing of indications and memorized values and unlatching of
output contacts, will clear the fault records, after which the sequence number will
start from 1 again.
Event records
Modbus events are derived from SPA events. With a few exceptions, SPA events
update binary points in the DI and the packed HR area. Simultaneously, a
corresponding Modbus event record will be generated. The event record contains the
Modbus DI/CO data point address and the value to which the point has changed
(0 or 1). SPA events lacking a corresponding DI/CO data point are shown as SPA
channel and event code (informative event) in the event record. The maximum
capacity of the Modbus event buffer is 99 events. The time stamp of Modbus events
is extended to contain complete information, from date to millisecond. To read an
event record:
1. Write a preset single register command (function 06) to HR671 using a selection
code as data value.
2. Read the selected fault record (function 04) from HR672, register count 8.
Alternatively, a fault record can be read using one command (function 23) only.
Selection code 1: reading the oldest unread record
Status register 3 (HR403) informs whether there are unread event records (see Fig.
4.1.15.2.-2). If there is one or several unread event records, the master can read the
contents using selection code 1.
The event record contains a sequence number which makes it possible for the master
to determine whether one or several unread event records have been deleted due to
overflow by comparing it to the sequence number of the previously read event
record.
The slave keeps track of which event record is currently the oldest unread. The
master can continue reading event records for as long as Status register 3 indicates
that there are unread records.
Special case 1: If there are no unread event records, the contents of the last read
record will be returned. If the buffer is empty, however, the registers will contain
only zeros. This is the only time when sequence number zero will appear.
Special case 2: If the master tries to read the next unread event record without
entering selection code 1 again, the contents of the last read record will be returned.
REF 610
79
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