Measurand Registers; Register Value Update - ABB Remote I/O RIO600 Installation And Commissioning Manual

1MRS757488 H
7.1.16
7.1.17
RIO600
Installation and Commissioning Manual
Modbus query for a
Binary Data point X
Instantaneous
Use the latest
instantaneous value
GUID-0CA80B7D-0544-473D-9452-419F25C5D4FF V1 EN
Figure 89: Latching mechanism for reading binary input data

Measurand registers

The Modbus measurands are located in the Modbus register area. The measurands are
readable from 3X and 4X areas from the same register addresses. The Modbus
measurands derive from the IEC 61850 filtered measurand values. Modbus register
values are always in integer format. Since the internal IEC 61850 values are
represented as decimal numbers, the Modbus stack needs to scale these values to
integer format. Thus, a scale factor always exists for each Modbus register value and
the same is mentioned against each Modbus addressable data point in the Modbus
point list manual.

Register value update

The Modbus register values can be updated in different ways. The update method is
predefined and fixed.
• The Modbus register values are available so that the Modbus stack directly reads
the momentary value of the mapped source object. These values are never cached
in the Modbus database. They are only fetched from the source object at the time
of the Modbus client reading. Most of the registers are mapped in this way.
• If the binary input read mode is latched, the Modbus stack reads the value cached
in the Modbus database, in case there is a change in value of the queried binary
input data point since its last poll.
Modbus TCP communication
Is the mode
Latched
Latched or
Instantaneous?
Was there a change
in the value of the
No
Binary data point X
since the last poll
made by the Modbus
master for this data
point?
Section 7
Yes
Use the latched value
175