AO N Updates (triggered) with 2 buffers, how to do ?

[K]

Hello,

I would like to use PCI-6731 board and traditional DAQ to generate N updates (triggered). I need to use 2 buffers filled with 2 different waveforms before start the generation (to avoid speed problems). I know how to fill these buffers (VI AO Buffer Write - in advanced analog output) and give them numbers (1,2).

The problem is that I don't know how to tell to the AO Start VI which buffer it should take (the 1st or the second).

I tried to open AO Start VI to modify the low level functions and I found the "staging list", on which the buffer number is specified. So I made external connectors in order to modify this information. Normally, I can change the array specifying the buffer number. But when I enter the buffer number to this array, I have an error message :

NI-DAQ LV: The specified device does not support the requested action (the driver recognizes the device, but the action is inappropriate for the device).

What should I do to use 2 buffered analog output ?

Any ideas and suggestions welcome, thank you !!!;-)
K.

NB : using Labview 7.1.

[Marc L.]

Hello,

First the use of different AO buffers is only possible when you use interruptions to transmit data and for several AO channels.
In the default case (your case) you have to use only one buffer.
The first advice I could give you would be to program with DAQmx drivers which are more efficient and more simple to use.
Then you have to find an other solution :
What do you want exactly to obtain on your AO channel ?
Why don't you filled your buffer with the two concatenated waveform ?

regards,

Marc Larue
NIF

[K]

Thak you for the help. I finally solved the problem creating one buffer with 2 different waveforms and a portion of silence between, so that I arrive to 20 generations per s. Thanks a lot, I didn't know that the "double buffered generation" was not possible with DMA transfert.