USB-6259 continuous digital input gives -200010 onboard buffer overflow error

[Ganeshs]

I am using Cont Read Dig Chan-Ext Clk.vi to perform continuous digital input on USB-6259.  I am using 20MHzTimebase clock source to perform a 32-bit digital input on Port0.  I tried various sample rates from 1k to 100k.  Also changed the "sample to Read" parameter from small (100) to large (5000).  In all cases, I get -200010 buffer overflow error.  I changed the data transfer mechanism to USB bulk but that did not help either.

Any suggestions?

Thanks.

[Jordan F]

Hi Ganeshs,

All M series devices (such as the USB-6259) do not have the ability to divide down a timebase to create an internal digital sample clock for acquisition (M series user manual page 100).  If you are using the 20MHz timebase as the clock source, your routing the 20Mhz timebase signal to the source of the digital sample clock.  Since this can not be divided down to a lower frequency, changing the rate input of the sample clock vi will not change the sampling rate of the digital task. Setting the sample rate for the digital sample clock only configures the buffer size and calculates the dt component of the waveform. 

The PCI-6259 manual states that the maximum sample rate is 1MHz (system dependent) for a Digital Input task with USB.  So, you can not sample over this value or you will experience a buffer overflow when sampling continously.  This is why you were seeing the error -200010.  

NI 625x Specifications (Page 7)

http://digital.ni.com/manuals.nsf/websearch/210C73CBF91128B9862572FF0076BE85
 
If you are trying to sample your digital signal at 1k or 100kHz, I would recommend to either use the AI sample clock or the CounternInternalOuput as the sample clock source.  This way you could specify the sample rate of your digital task.  To use either of these as the sample clock source though you must create a dummy AI or counter task to access the clocks.  The Correlated Dig Read with Counter.vi example below is a good place to start.  This example can be found in the NI Example Finder under Help»Find Examples»Hardware Input and Output»DAQmx»Digital Generation.  It uses the internal counter as the sample clock for the digital task.  

The M series user manual (page 100) is a good reference to find the valid sample clock sources for your digital task.  

M Series User Manual (Page 100)

http://digital.ni.com/manuals.nsf/websearch/2025C99AB0614F9E8625748000577B9A

Message Edited by Jordan F on 06-26-2009 06:44 PM