Accessing onboard buffers on PXI-7344

[rYan7]

Hi all together,

I have a problem with understanding the usage of buffers on the NI PXI-7344 Motion Controller.

My aim was to write an onboard program that continously reads the current axis position and saves it to a buffer. The host computer should then from time to time read a set of data from that buffer and save it. But I could not manage to access the buffer via the host computer. Is it only possible to read buffers created by onboard programs with exactly those programs and buffers created by the host only with the host computer?

I have already read by looking at other posts that onboard programs are not a good solution to get accurate time sampled data. The problem in my case is that the number of points to acquire is not fixed, but detemined at run-time, so using flex_acquire_trajectory_data cannot be used (or can it in some way?).

Futhermore i have to acquire data from a DAQ device, but i have not thought about that yet. I hoped to complete the motion thing first.

Putting it all together i want to control my steppers and acquire time-sampled data from the motion controller and the DAQ device. The data should combine to one big set, where every position/velocity data has an equivalent DAQ data part and vice versa.

In my system I use an PXI/SCXI-Chassis (PXI-1050) with PXI-7344 Motion Controller and PXI-6221 as DAQ. The system is connected via fiber cable with my PC.

Motion system is open-loop without encoders.

I am using the C library for programming.

Any help or suggestions would be appreciated.

Thanks

rYan

[Jochen]

rYan,

I strongly recommend to abandon the onboard buffer approach. As you need correlated DAQ and position data, I'd like to suggest to acquire the positions also with your DAQ device. To do so, you could route the encoder signals to the PXI trigger lines and use them for a buffered position measurement with your DAQ device.

Here is some more information about this topic.

I hope this helps,

Jochen Klier

National Instruments