compactDAQ Encoder + Voltage using same sample clock

[Jed_Davidow]

I am running a little blind here, as I need to code before I have all of my hardware available.

I have a cDAQ 9172 with two analog modules (9205 + 9219) and a 9401 digital module.

I willbe perfomring externally timed voltage and angular encoder positioning.  I have example code for both, and don't see a general problem there.  However, I have three questions that I can't find answers for in the documentation...

1) The 9401 pinout lists both SRC/GATE and A/Z/B connections.  On M-Series boards and DAQmx, a quad encoder is connected to the SRC and GATE.  Does that also hold true for the 9401 on cDAQ?  Or does something magical happen in the driver so that I have to connect to the A and B (Z unused)?

2) If the 9401 is set up with two counters, can I use the remaining pins as the EXT CLK connection?  Or should I put the 9401 in slot 5 and the 9205 in slot 6 and use PFI0 on the 9205as the EXT CLK input?

3) Regardless of which one I use in (2) above, I assume that I can specify the same PFI channel as the EXT CLK on multiple tasks (encoder counts, voltage sampling, digital sampling).  True?

Thank you!

[John_P1]

Hi Jed,

Thanks for posting. For most purposes, you can think of the 9172 as an M Series DAQ with modular front-ends. To answer your immediate questions:

1) Technically, the M Series counters actually do use A and B inputs (see the counters section of the M Series User manual on page 7-1). regardless of this, the pinout you are referring to simply lists the default pins on the 9401. If you have the 9401 in slot 5 or 6, you may use the digital lines as PFI lines exactly the same was as you would an M series. I always like to explicitly state which lines I am using in my tasks to avoid confusion, so the pinouts wouldn't even be relevant in this case.

2) There is no problem with using the extra lines on the 9401 for your EXT CLK connection (provided it is in slot 5 or 6). Again, the 9401 is essentially giving you access to the PFI lines that would be on an M series--any of these lines can be used interchangeably. As I understand it, you can't use the PFI line on the 9205 in a 9172 chassis, according to the KnowledgeBase Using the Digital Output and PFI Lines of the NI 9205/9206 with Compact DAQ.

3) You can route the EXT CLK signal from the 9401 to be used for as many tasks as you like. Keep in mind that to do hardware-timed digital I/O you would need a correlated module (such as the 9401) in slot 1, 2, 3, or 4. These slots function as port 0 on an M series (5 and 6 take the place of port 1 and port 2). On an M series, port 0 is the only port to support correlated digital I/O.

So, if you are familiar with M series boards or have existing code for an M series, it should be fairly easy to use with a Compact DAQ provided you have the necessary modules. If you run into any specific issues or have any other questions please don't hesitate to post back and let us know. Thanks!

-John

Message Edited by John P on 07-02-2009 07:48 PM

[Jed_Davidow]

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John P wrote:

3) You can route the EXT CLK signal from the 9401 to be used for as many tasks as you like. Keep in mind that to do hardware-timed digital I/O you would need a correlated module (such as the 9401) in slot 1, 2, 3, or 4. These slots function as port 0 on an M series (5 and 6 take the place of port 1 and port 2). On an M series, port 0 is the only port to support correlated digital I/O.

So I cannot use the 9401 in slot 5 (that's already being used as the encoder interface and the Ext Clk interface) to perform an internally clocked DI acquisition?

Is there a matrix with the cDAQ "rules" somewhere?  🙂

(Thanks for your timely reply)

[John_P1]

Hi Jed,

Unfortunately, this is the case--you would need a 9401 (or other correlated module) in slot 1-4 to do the clocked DIO.

One good place to find information about cDAQ would be the 9172 User Guide and Specifications. It turns out there actually is a matrix on page 35-36 that shows the rules for the Digital I/O in the cDAQ chassis.

Also, the follwing KnowledgeBase is a good reference to see which modules are correlated and which are static:

C Series Modules Supported in the NI-cDAQ 9172 CompactDAQ 

-John

Message Edited by John P on 07-02-2009 08:50 PM