"Selected lines do not support buffered operations" error for PXI-6251 PFI lines

[kekin]

Hi all,

I want to use PFI lines i.e. port 1 &2 of PXI-6251 to generate the digital pattern which are triggered by an external event or by an internal counter output.

BUt since PFI lines do not support Hardware timing, what is the work around for it.

My Port 0 is already used for other purposes & I have to manage it with PFIs only.

My requirement is:

An input 400Hz square wave should trigger the waveform generation on the PFI lines. Each waveform is unique & should start on the rising edge of the input square wave signal. All the PFI lines will generate 400Hz waveform with different phase shift & duty cycles.

I am done with the logic of generating different phase shifts & duty cycles. But "Selected lines do not support buffered operations" error arrives when I try to use "SAMPLE CLOCK" triggering for PFI configured as DIGITAL OUPUT task.

Request to suggest any other methods to meet my requirements with these PFI lines only.

[John_P1]

Hi kekin,

Unfortunately, the PFI lines don't physically support clocked DIO Waveform operations.  They are used either for static DIO or as lines that let you route timing / triggering signals (including connecting to the on-board counters).  As you have already noticed, there are only 2 counters available on M Series DAQ devices which does not give you enough lines.

Are you open to a hardware addition or replacement? 

Many boards have 32 lines on port 0 (these typically require a second 68-pin connector to connect to the extra 24 HW-timed lines).  Examples of this in PXI form factor are the 6224, 6254, or 6259. 

The lowest cost option for adding an additional 8 HW-timed DO lines to your PXI system is most likely through a second board--i.e. the PXI 6220.  If slot availability or future expansion is a concern, I'd recommend one of the above boards that have 32 clocked DIO lines.

Best Regards,

[Rob31]

Hi,

I am actually trying to acquire encoder digital signals (signal A and B) with SSI and I use Port0/line2 (32bits) to get the digital signal A from the encoder. However, I am not sure I have extra 32bits to get the digital signal B from the encoder. So do you have a solution ? Do I have to buy a card to get the digital signal B from the encoder ?

Thanks,

[Kevin_Price]

I think you have some misunderstandings:

- if you have A and B channels from your encoder, you likely should be thinking about *quadrature*.  You'd use a counter-based position measurement task, you'd wire into PFI pins (not port 0), and you'd have only 2 (or maybe 3 if you also have an index pulse, commonly called Z or I) signals to connect not 32+.

- SSI wouldn't normally be implemented on a DAQ board, you'd use something with dedicated SSI hardware.  Analogous to RS232 serial.

You posted the entire product catalog but didn't identify the model #, including the interface & signal options.  Which device do you have *specifically*?   Also, what DAQ board(s) do you have available?

Multifunction boards like the 6251 in this old thread's title support single-ended quadrature directly.   If your signals are differential, you'd either need a 3rd party converter or a different DAQ device (probably cDAQ).

SSI isn't commonly supported on DAQ boards.  I can't really point you anywhere specific because I haven't really dealt with it directly myself.

-Kevin P

[Rob31]

Hi,

This is the encoder Zettlex 58mm 16-bit IncOder (cf datasheet). I have underlined the corresponding device in the datasheet but you can find the information from this part number: P/N INC-11-58.100-161001-SSI1-RC2-24CT-S-V.

I have the NI6343. I think it is possible to acquire SSI1 with it. I have already generated the corresponding chronogram and it works (tested with the oscillo). But, for the DO acquisition (Signal A and B underlined in the Datasheet of the encoder) I am not sure to manage the acquisition of both signals since it require to buffer two signals... that's why my question.

Thanks,

Regards,

Robin

[Kevin_Price]

I still think there may be some pending issue awaiting because your device deals in single-ended digital signals while the SSI spec is based on differential.

To my reading, you have to pick 1 and only 1 kind of signal interface.  You can have absolute SSI encoding with clock and data signals *OR* you can have incremental quadrature encoding with A,B,Z signals.  Not both at once.   From your model #, it's clear you have SSI, not ABZ.

Your original question referred to 32 bits but I don't know why.  You say you've already figured out how to generate the chronogram timing you need.  That's good news, the rest of the things you need to do should be pretty straightforward once you get the timing worked out.

About all that's left is to use your timing signal to sample the Data signal, then assemble that sequence of bits into a meaningful angle measurement.  You probably need to convert the Data from differential to 5V single-ended digital, but you'll only need 1 of the many lines on port 0 of your DAQ board to do your sampling.

-Kevin P