National Instruments NI-DNET Accessing I/O Members in LabVIEW

Chapter 4 NI-DNET Programming Techniques
NI-DNET User Manual 4-10 ni.com
By consulting the specifications for the Control Supervisor object and the
AC/DC Drive object, you can determine that the DeviceNet data type for
Run Fwd and Fault Reset is BOOL (boolean), and the DeviceNet data type
for Speed Reference is INT (16-bit signed integer).
Accessing I/O Members in LabVIEW
Many fundamental differences exist between the encoding of a DeviceNet
data type and its equivalent data type in LabVIEW. For example, for a
32-bit integer, the DeviceNet DINT data type uses Intel byte ordering
(lowest byte first), and the equivalent LabVIEW I32 data type uses
Motorola byte ordering (highest byte first).
To make it easier for you to avoid these data type issues in your
LabVIEWapplication, NI-DNET provides two functions to convert
between LabVIEW data types and DeviceNet data types:
ncConvertForDnetWrite and ncConvertFromDnetRead. These
functions are used to access individual members of an I/Oassembly using
normal LabVIEW controls and indicators.
The following steps show an example of how you can use
ncConvertForDnetWrite to access the Basic Speed Control Output
Assembly described in the previous section:
1. Use the NI-DNET palette to place ncConvertForDnetWrite into
your diagram.
2. Right-click on the DnetData in terminal and select Create
Constant, then initialize the first 4 bytes of the array to zero.
3. Right-click on the DnetType terminal and select Create Constant,
then select BOOL from the enumeration.
Table 4-1. Attribute Mapping for Basic Speed Control Output Assembly
Member
Name
Class
Name Class ID Instance ID
Attribute
Name Attribute ID
Run Fwd Control
Supervisor
29 hex 1Run1 3
Fault
Reset
Control
Supervisor
29 hex 1FaultRst 12
Speed
Reference
AC/DC
Drive
2A hex 1SpeedRef 8