Frame Input Queued Mode

NI-XNET 19.1 Help

Edition Date: June 2019

Part Number: 372841W-01

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This mode reads data from a dedicated queue per frame. It enables your application to read a sequence of data specific to a frame (for example, a CAN identifier).

You specify only one frame for the session, and nxReadFrame returns values for that frame only. If you need sequential data for multiple frames, create multiple sessions, one per frame.

The input data is returned as an array of frame values. These values represent all values received for the frame since the previous call to nxReadFrame.

Example

In this example network, frame C is a cyclic frame that transmits on the network once every 2 ms. Frame E is an event-driven frame. For information about cyclic and event-driven frames, refer to Cyclic and Event Timing.

Each frame contains two signals, one in the first byte and another in the second byte.

This example uses CAN. The following figure shows a timeline of a frame transfer on the CAN network, followed by two calls to nxReadFrame (one for C and one for E).

The following figure shows the data returned from the two calls to nxReadFrame (two different sessions).

The first call to nxReadFrame returned an array of values for frame C, and the second call to nxReadFrame returns an array for frame E. Each frame is displayed with CAN-specific elements. For information about the data returned from the read function, refer to Raw Frame Format. The example uses hexadecimal C and E as the identifier of each frame. The first two payload bytes contain the signal data. The timestamp represents the absolute time when the XNET interface received the frame (end of frame), accurate to microseconds.

Compared to the example for the Frame Input Stream mode, this mode effectively sorts received frames so you can process them on an individual basis.

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