1MAC052634-MB D
Section 3
Vendor-specific implementation
615/620 series ANSI
19
Communication Protocol Manual
momentary position bit and the MCD bit of a certain indication point always occur as pairs
in the Modbus memory map.
Observe that the MCD bit states are client dependent. The MCD bit is only reset for the
specific Modbus client that reads it. Thus, other Modbus clients may still receive value one
from the same MCD bit when it is read.
MOM indication changes are captured in the IED's sequential Modbus event buffer.
Additionally, the Modbus event buffer provides a time stamp and chronology of indication
changes.
3.3.4.1
Multiple digital inputs mapping
Digital inputs related to two-bit DPC or DPS objects, for instance circuit breaker and
disconnectors, have a multiple mapping in the Modbus address space. The objects’ open
and close bits are coded as MOM+MCD bit pair entities. The MCD bits reveals if the
object has changed its position several times since the Modbus master last scanned it. In
addition, the open and close bits are also coded using MOM values only, among with a
fault bit. The fault bit is set to “1” when the object is in intermediate (00) or faulty (11)
position.
Table 9:
Bit treatment
The MOM values are identical in each entity. The MCD bit is only reset if the MOM bit
in the same entity is read.
3.3.5
Measurand registers
The Modbus measurands are located in the Modbus register area. The measurands are
readable from 4X areas.
The formula for calculating the Modbus register value is:
(Equation 1)
The range of the original IEC 61850 value can be seen in the Modbus memory map point
list.
Bits
Treatment
Close MOM
One 2 bit entity
Close MCD
Open MOM
One 2 bit entity
Open MCD
:
Close MOM
One 1 bit entity
Open MOM
One 1 bit entity
Faulty position MOM
One 1 bit entity
:
Modbus value
IEC
Value scaleFactor
Offset
=
×
(
)
+
61850
