default data transfer mechanism

[sxs707]

Hi,

Currently I have PXI-6259 card, LabWindows/CVI 8.0 and DAQmx running on Windows XP.   I am a newer to the DAQ. I have some following questions about the data transfer mechanism from the FIFO on the DAQ card to computer memory.

1.There are all DMA, interruputs and programmed I/O data transfer mode for AI,AO,DI,DO. How can I determinde which one should I choose when I do a task? And what is the default data transfer mechanism for the PXI-6259?

2.From the NI625x specifications I see there are only 6 DMA channels, just as bellow:

DMA channels
(PCI/PCIe/PXI/PXIe devices) .........6, analog input, analog output, digital input, digital output, counter/timer 0, counter/timer 1.

What does that mean? Is it that there are only 6 DMA channels for all of the AI, AO, DI, DO and Couner0/1?

Thanks!

Guo

[Christian Mergl]

Hey,

The default transfer mechanism is DMA. IRQ and programmed I/O doesn't give you the ability to transfer data at high rates, so I would suggest to NOT change the transfer mechanism to one of thoose.

Christian

[John_P1]

Hi Guo,

Regarding the 6 DMA channels available, I just wanted to point out that there is one DMA channel available for every possible task you can run (AI, AO, DI, DO, and 2 Counters).  Each individual AI/AO channel does not use its own DMA channel, but rather the task reserves the DMA channel.

So, on an M series you will never run out of DMA channels since you cannot run more than 6 tasks at once.  Some of our older boards do not have a DMA channel available for each task, so the user would have to decide which tasks required the use of DMA. 

Your tasks will default to use DMA--unless you are having specific problems with the DMA controller on your computer, I can't think of any good reason to change to Interrupts.

-John