PXI 6221 Maximum Digital Input Sample Frequency

[mvr]

I need some help with the specs for high speed digital input operation of a PXI-6221 in a PXI chassis running from a PCI-Express MXI controller.

I am looking at the 622X Specifications Sheet trying to determine the maximum digital input scan rate that can be achieved.  In the section on Digital I/O/PFI the DI Sample Clock is listed as 0-1MHz.  Is that the maximum for an externally applied signal or can I run at a faster rate if using clock generated internally by a counter? 

Why are Port 0 P0.<0,1> specified differently under waveform characteristics?  Do these two pins work differently than the rest of Port 0 on the 6221 for digital input or is that listing only for high speed digital output operation?  The port sample size is listed as up to 8 bits for a 6221, this implies that all 8 bits of Port 0 can be used as high speed digital inputs. 

[Matt_A]

Hello mvr,

Let me try to answer your questions in order:

"In the section on Digital I/O/PFI the DI Sample Clock is listed as 0-1MHz.  Is that the maximum for an externally applied signal or can I run at a faster rate if using clock generated internally by a counter?"

Yes, 1MHz is the maximum sample rate for Digital Acquisition on this device regardless of whether the clock source is internal or external. You cannot attain a sample rate faster than 1MHz by using a counter.

"Why are Port 0 P0.<0,1> specified differently under waveform characteristics?"

Port 0 P0.<0,1> are specified differently for the 37-pin NI PCI-6221. This device (which is only available for the PCI bus) only has 2 clocked digital lines, as opposed to the 68-pin NI 6221 which has 8 clocked digital lines and is available for both the PXI and PCI interfaces. I hope this information is helpful. Let me know if anything is unclear.

[mvr]

Thanks for the reply Matt.

The NI 622X specification document on page 6 groups the NI-6221(68 pin) with the PCI-6221 (37 pin) in the waveform characteristics section.  Kind of confusing as it looks like it should be grouped with the NI6225.  Thanks for clearing that up I really appreciate it.

Message Edited by mvr on 04-13-2007 08:22 AM

[Matt_A]

Hello mvr,

You are absolutely correct, that document does appear to be confusing.

This was reported to R&D (# 48F95IAH) for further investigation.

Let me know if you have any other questions.