Daqmx Write Block

[Tan_godo]

Hi ,

The scenario is i have an analog daq card with about 16 channels , my requirement is such that

i need to have some continous data generation on 2 channels .But they will be triggered independant of each other and not simultaneously.

So what happens is the Daqmx write block gives out this error code "-50103 " i.e. "NI Platform Services: The specified resource is reserved. The operation could not be completed as specified."

Is there any way to use 2 channels for continous generation

Regards

Tan

[Mark Smith]

You can use two channels for continuous generation, but you generally cannot have two tasks (which you would need to have to enable two separate triggers) on one subsystem - this is from the DAQmx Help:

"For most devices, only one task per subsystem can run at once, but some devices can run multiple tasks simultaneously."

What they mean by subsystem is the AO or the AI or the counter on a general purpose DAQ device. So you can have independent AO and AI in two tasks, but not two AO tasks.

So, if you only have one card available, you'll have to figure out something else. For instance, if the offset between signals is constant (or can be set before the generation begins), you could create a two channel signal where one is just padded with zeros until it needs to start. If you really need a second signal to start at an arbitrary time, you'll probably need another card.

Mark

[Neville D]

Hi ,

The scenario is i have an analog daq card with about 16 channels , my requirement is such that

i need to have some continous data generation on 2 channels .But they will be triggered independant of each other and not simultaneously.

Regards

Tan

What card do you have? The cheaper E Series cards have limited DMA channels, and sometimes that can be the reason why you can't get two AO channels at different rates out at the same time.

What are you outputting to the daq channels? Is it buffered? If the rates are not too fast and non-buffered, you could output both the channels software-timed in the same loop.

Neville.

[Mark Smith]

What card do you have? The cheaper E Series cards have limited DMA channels, and sometimes that can be the reason why you can't get two AO channels at different rates out at the same time.

What are you outputting to the daq channels? Is it buffered? If the rates are not too fast and non-buffered, you could output both the channels software-timed in the same loop.

Neville.

I'm not sure if DMA channels are the limiting factor - I would think that you can't have more than one AO rate because on most systems you can only have one sample clock for the AO generation. Most DAQ devices will have a single AO buffer. The DACs get data from the buffer on each sample clock tick so all of the DACs get data (and generate data) at the same rate. This is true for hardware timed generation. I can't comment on software timed as I don't use it (except for static voltages).

Mark

[Tan_godo]

Hi ,

i am basically Using a cDAQ 9264 . on an 8 slot USB Daq chassis.

@ mesmith : i already tried out by creating a 2 channel task using " Dev1/a01:2 " , giving some zero signal data on 1channel and the actual data on the other .But in this case i will have to use the daqmx write block as " n channel n sample " , so accessing any other channels i.e other than 1and 2 will give me an error that the device is reserved.

So i will have to think of some else since getting new card is not possible .

Regards

Tan