how to validate Digital input read speed clocked by RTSI line?

[braver]

how to validate Digital input read speed clocked by RTSI line, such as eample "CDI Single Point clocked by Counter (E).vi". I try to use the template "NI Timestamp Code Timer.vit" to test the highest speed I could use with PXI6733 and find the highest reading speed could achieve is 20kHZ. But PXI6733 is supposed to reach 20MHz, how can I do to get higher speed? And what's the highest frequency we could specify for counter0 in PXI6733?

[Jeremy_C]

Braver,

The onboard buffer of the PXI-6733 is what allows for the 10MWords/s transfer rate when doing hardware timed, buffered digital I/O. However, it appears like the test you were running was not utilizing the onboard buffer. Instead you are reading one point at time, which means you are making a driver call for every point. This is very slow as compared to reading 100 points into the onboard buffer and then making one driver call to request all 100 points at one time. This utilizes the onboard buffer and allows you to make much faster acquisitions. You can use the internal clock on the PXI-6733 or an external clock to reach your maximum rate of 10MHz. The maximum frequency pulse train your counter can generate is 5MHz. I hope this information hel
ps.

Jeremy C
Applications Engineer
National Instruments

[braver]

Jeremy C:
Your answer is helpful. "You can use the internal clock on the PXI-6733 or an external clock to reach your maximum rate of 10MHz", could you give an example of this? "CDI Single Point clocked by Counter (E).vi" generate pulse train on counter 0, how do I know this is the clock use for Digital Input sample rate? Why we need RTSI 0 use that clock too? it seems we could cancel the RTSI part in this example.
And if I use buffer read on PXI6733, what's the constraint for buffer allocation? Any example on buffere preallocation?
Thanks
Braver

[Jeremy_C]

Braver,
Let me clarify a few things. First, the 6733 supports correlated digital I/O. This means that the digital operation does not have its own clock. You can correlate the digital operation with the AO clock, which will allow a digital operation up to the max AO rate. You can generate a pulse train with an onboard counter and use that as your digital clock source. Also, you can use a completely external clock source to achieve the max digital rate of 10MHz. The knowledge base, linked below, points you to a couple of examples that ship with LabVIEW. Be sure and read the documentation associated with each example.
Knowlege Base
As for
the example CDI Single Point clocked by Counter (E).vi, notice how the output of...