12
KNX serial card
+030220326- rel. 1.0 - 16.05.2017
ENG
5.2.1
Modbus Datapoint
For each variable that has been added, the “Modbus Datapoint” sub-
menu shows certain data that cannot be modified: Modbus type (holding
register, coil, input register, input), read/write address, and the number of
consecutive registers making up the parameter. In the same sub-menu,
the endianness field can be set so as to specify the order of bytes in the
Modbus parameter. The options are big or little endianness for 16-bit
data, there are four options (big, little, big swapped, little swapped) for
32-bit data, while no options can be selected for 1- or 8-bit data.
The default value for this field is big endian.
5.2.2
Value Conversion
The “Value Conversion” sub-menu shows the type (non-modifiable) of
value represented by the Modbus parameter (Boolean, signed integer,
unsigned integer, floating), while the remaining fields specify:
•
Bit Position: position of the least significant bit in the Modbus register
(values between 0 and number of bits in the register – 1)
•
# of Bits: number of bits in the Modbus register
The # of Bits field shows the initial size of the Modbus parameter, this
must be decreased if setting the Bit Position parameter to a value other
than 0. The sum of the Bit Position parameter and the new # of Bits setting
must coincide with the initial value.
The other fields in the “Value Conversion” sub-menu depend on the type
of datapoint selected subsequently. If the selected KNX datapoint is type
1.xxx, the “Value Conversion” sub-menu shows the following fields:
•
Truth value: when reading Modbus parameter X, the KNX datapoint Y
will be: Y = (X == truth value). The default for the truth value is 1.
•
Invert boolean: when set to No, no other changes are made to Y,
otherwise when set to Yes, Y is inverted. The default is No.
In all other cases, the following fields can be set:
•
A, B: allow linear conversion on the data. With the value of the Modbus
register being X, the converted value Y = A * X + B. Vice-versa, if
reading from KNX, the Modbus value is determined using the rule X
= (Y - B) / A. The default values of A and B are 1 and 0 respectively (no
transformation).
•
Rounding: method for rounding off the result of linear conversion.
The method adopted by default is the nearest whole number. Other
methods available are: up, down, towards 0, away from 0.
5.2.3
KNX Datapoint
The “KNX Datapoint” sub-menu is used to associate the type of KNX
datapoint, choosing from the available options in the KNX Type drop-
down menu.
The transmission mode can also be selected, from one of the following
three options:
•
No send, the datapoint is not never sent independently over the KNX
bus,
•
On change, the datapoint is sent again over the KNX bus whenever it
changes, irrespective of the extent of the change
•
On difference, the datapoint is sent again over the KNX bus whenever
it changes by absolute value more than a certain amount, selectable in
the Sending Difference field (default 1).
Cyclical transmission mode can also be selected for a datapoint,
specifying the period in seconds, in the Interval field (default 1s).
Special attention must be paid when needing to define a 16.xxx
character string datapoint. In this case, the mapping table associated
with the datapoint also needs to be specified (choice between 1 of the 8
available). The mapping table is defined in the “String Tables” menu.
5.3 “String Tables” menu
The “String Tables” menu is used to define the mapping tables for
type 16.xxx KNX parameters (character strings). The fields in this menu
therefore depend on whether there is a type 16.xxx datapoint: if there
are no datapoints of this type, proceed with the next step. For each of
the tables referred to in the “Datapoint Settings” menu, the number of
items in the table needs to be specified, and for each item in the table the
datapoint value needs to be mapped to the required string.
Fig. 5.g
Once all of the datapoints have been configured, these are available in
the ETS Devices menu; the datapoints can then be associated with the
corresponding group addresses, following the standard procedure in
ETS5. Subsequently, the individual address can be assigned to the card
and the configuration for the corresponding device can be downloaded.
