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REF 610
78
Feeder Protection Relay
Technical Reference Manual
Note!
If an "Illegal data value" exception response is generated when attempting to preset
multiple registers, the contents of the register to which an illegal value has been
imposed and of the following registers will not be changed. Registers which have
already been preset will not be restored.
User-defined registers
Reading of unwanted data in a data block wastes bandwidth and complicates data
interpretation. For optimum efficiency in Modbus communication, data has
therefore been organized into consecutive blocks. In addition, a set of programmable
user-defined registers (UDR) has been defined in the holding register area.
The first sixteen holding registers, i.e. HR1...16, are user-defined registers. The
UDRs can be linked to any holding register, except for HR721...727, using SPA
parameters 504V1...504V16. However, one UDR cannot be linked to another, i.e.
linking cannot be nested. Each parameter contains the address of the holding register
to which the UDR is linked.
If a UDR is linked to a non-existent holding register, reading from the register will
fail and an "Illegal address exception" response will be sent. Giving the link address
the value 0 will disable the UDR. If the master reads from a disabled UDR, the value
0 will be returned.
The UDRs are mirrored in HR385...400.
Fault records
The data recorded during a fault sequence is called a fault record (FR). The slave
stores the five latest fault records. When a sixth record is stored, the oldest record
will be deleted. To read a fault record:
1. Write a preset single register command (function 06) to HR601 using a selection
code as data value.
2. Read the selected fault record (function 04) from HR601, register count 28.
Alternatively, a fault record can be read using one command (function 23) only.
Selection code 1: The master reads the oldest unread record
Status register 3 (HR403) informs whether there are unread fault records (see Fig.
4.1.15.2.-2). If there is one or several unread fault records, the master can read the
contents using selection code 1.
The fault record contains a sequence number which makes it possible for the master
to determine whether one or several unread fault records have been deleted due to
overflow. The master compares the sequence number to that of the previously read
fault record.
The slave keeps track of which fault record is currently the oldest unread. The master
can continue reading fault records for as long as Status register 3 indicates that there
are unread records.
Special case 1: If there are no unread fault 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.
1MRS 755310
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