Other explicit messaging services, Other explicit messaging services -13 – National Instruments NI-DNET User Manual

Page 44

Chapter 4

NI-DNET Programming Techniques

4-13

NI-DNET User Manual

easiest way to execute the Set Attribute Single service on a remote device
is to use the NI-DNET

ncSetDnetAttribute

function.

For a given attribute of a DeviceNet device, you need the following
information to use the

ncGetDnetAttribute

ncSetDnetAttribute

function:

•

The class and instance identifiers for the object in which the attribute
is located

•

The attribute identifier

•

The attribute’s DeviceNet data type

You can normally find this information from the object specifications
contained in the DeviceNet Specification, but many DeviceNet device
vendors also provide this information in the device’s documentation.

For the C programming language, the attribute’s DeviceNet data type
determines the corresponding NI-DNET data type you use to declare a
variable for the attribute’s value. For example, if the attribute’s DeviceNet
data type is

INT

(16-bit signed integer), you should declare a C language

variable of type

NCTYPE_INT16

, then pass the address of that variable as

the

Attr

parameter of the

ncGetDnetAttribute

ncSetDnetAttribute

function.

For LabVIEW, the attribute’s DeviceNet data type determines
the corresponding LabVIEW data type to use with the

ncConvertForDnetWrite

ncConvertFromDnetRead

functions. The

ncConvertFromDnetRead

function converts a DeviceNet attribute read

using

ncGetDnetAttribute

into an appropriate LabVIEW data type. The

ncConvertForDnetWrite

function converts a LabVIEW data type into an

appropriate DeviceNet attribute to write using

ncSetDnetAttribute

. For

more information on these LabVIEW conversion functions, refer to the

Using I/O Data in Your Application

section.

Other Explicit Messaging Services

To execute services other than Get Attribute Single and Set Attribute Single,
use the following sequence of function calls:

ncWriteDnetExplMsg

ncWaitForState

ncReadDnetExplMsg

. The

ncWriteDnetExplMsg

function sends an explicit message request to a remote DeviceNet device.
The

ncWaitForState

function waits for the explicit message response,

and the

ncReadDnetExplMsg

function reads that response.

Use

ncWriteDnetExplMsg

for such DeviceNet services as Reset, Save,

Restore, Get Attributes All, and Set Attributes All. Although the DeviceNet