DeviceNet NI-DNET User Manual

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Chapter 3 Developing Your Application

2. Call the ncWaitForState function with the DesiredState

parameter set to

Read Available. This function waits for output

data to be transmitted and for new input data to be received. If your

application is multitasking, you might have other tasks to do in your

application while you wait for new input data. If so, use the

ncCreateNotification or ncCreateOccurrence function

instead of

ncWaitForState (refer to Step 2. Start Communication).

3. Call the

ncReadDnetIO function to read input data received from the

DeviceNet network.

4. Loop back to step 1 as needed.

Complete the following steps with an Explicit Messaging Object:

1. Call the

ncWaitForState function with the DesiredState

parameter set to

Established. This ensures that the explicit message

connection is established before you send the first explicit message

request.

2. To get an attribute from a remote DeviceNet device, call the

ncGetDnetAttribute function.

3. To set the value of an attribute in a remote DeviceNet device, call the

ncSetDnetAttribute function.

4. To invoke other explicit message services in a remote DeviceNet

device, use the

ncWriteDnetExplMsg function to write the service

request, the

ncWaitForState function to wait for the service

response, and the

ncReadDnetExplMsg function to read the service

response.

5. Loop back to step 2 as needed.

Addition of Slave Connections after

Communication Start

If you need to add I/O and Explicit Messaging connections after the

communication on the network has started, you can call

ncOpenDnetExplMsg and ncOpenDnetIO as long as the Interface

Object’s poll mode had been configured to

NC_POLL_SCAN (Scanned) or

NC_POLL_INDIV (Individual). Since the Automatic poll mode

(

NC_POLL_AUTO) calculates the expected packet rate (EPR) based on the

estimated network bandwidth, all the I/O connections have to be opened

before you start the communication if the Automatic mode is selected. The

EPR restrictions due to different values of the

PollMode parameter still

apply to the I/O objects. For details on these requirements, refer to

ncOpenDnetIO and ncOpenDnetIntf function descriptions in the

NI-DNET Programmer Reference Manual.