Clock and Trigger configuration for PCI-5112.

[Roberto_N.]

Hallo, I need of informations about the behaviour of my NI5112 digitizer.
I’ve installed a PCI model with Labview 5.1 and Niscope, and I made some changes on “niscope ex fetch forever.vi” shipping example, due to make possible a continuous acquisition with different configurations:
1)Acquisition on one or both the analog channels,
2)10 MHz clock choice (internal or external on front PFI1 connector),
3)Trigger source choice (SW, Ch0, Ch1, Trig).

It’s all OK for both channels acquisition, but I don’t understand some things I saw about external clock and trigger.

External clock
I’ve inserted the “niscope Configure clock.vi” sub.vi immediately after the horizontal setting, wiring the integer “0” or “2” to the “input clock source” control, due to select "internal" or "PFI1" source, respectively.
When I run the program with a 10 Mhz TTL input (external clock) on PFI1 connector and the external input clock enabled, I see the acquisition is OK, but when I disconnect the external clock from PFI1, it seems the acquisition continues, without clock input!
Does the internal clock become active when the external one fails, or is there a configuration error?

Trigger
I’ve substituted the “Conf. Trigger Software.vi” with the “Conf. Trigger Edge.vi” sub.vi, so it is possible to select Ch0, Ch1 or Trig channel, wiring to “trigger source” control, the “0”, “1” or “VAL_EXTERNAL” strings, respectively.
When I set an “edge trigger” on Ch0 or Ch1, a single record of 1000 points is acquired (it’s right because it corresponds to default data on horizontal settings); after that acquisition stops (all zeroes fetching).
When I set an edge trigger on Trig channel, I see that there is no effect! Acquisition starts with or without the trigger source connected, and it indefinitely continues, as for the SW trigger setting.
Where is the error?

I’d like to know if is it possible a continuous acquisition without data loss (I cannot consider a multi-record acquisition, because there is a 100 usec not acquiring time between two consecutive records), starting at an edge of a trigger signal, with or without an external reference clock.
How can I perform that?

Thank you in advance.

[Josh H]

What version of NI-SCOPE are you using? NI-SCOPE 2.5 and later will give an error when the external reference clock becomes disconnected, but previous versions of NI-SCOPE will not report the error. As a side note, NI-SCOPE 2.5 is only supported on LabVIEW 6.1 and later.

As for your edge trigger question, I need some more information. Are you applying the same signal to teh Trig channel to trigger off of as you applied to Cho and Ch1? Also, I am a little confused as to what you are using the SW trigger for.

There is a way to a perform continuous acquisition with the NI 5112. Please see the example that ships with NI-SCOPE called niScope Fetch Forever. Let me know if you have any questions about that example.

[Roberto_N.]

I’m already using "niScope Fetch Forever” with modifications due to change clock source (from internal to external, on PFI1 connector) and trigger source (from SW to Ch0, Ch1 or Trig channels).

External clock:
I’m using Lv 5.1, with Ni-scope 2.1.4, and I don’t get any error if I disconnect the external clock signal during the fetch operation (moreover acquisition appears as still in progress, so I am not sure if ext. clock setting is correct).

Edge trigger:
I'm also interested to continuously acquire data from Ch0 and/or Ch1; this acquisition has to start when the edge of a single pulse signal occurs, and has to continue indefinitely, at a 3-4MHz sampling rate, without data loss.
Which modifications have I to make on "niScop
e Fetch Forever” example, to perform that?

Thank you.

[Josh H]

External clock:
Since you are using NI-SCOPE 2.1.4, you will not see an error or warning generated when you disconnect the external clock signal during fetch. The acquisition will continue, but the PLL will rail to the top or bottom of it's comparator since the 10 MHz reference clock is no longer there. NI-SCOPE 2.5 will report an error in this circumstance.

Edge trigger:
It is not possible to use an edge trigger AND acquire data continuously with the NI 5112. The concept of acquiring data continuously with the NI 5112 is that you don't want to receive a Reference (Stop) trigger. Once you receive a Reference (Stop) trigger, the board acquires it's necessary posttrigger samples and then stops acquiring data. The only way around this is to us
e the Acquisition Arm (Start) trigger. However, this trigger can only be a digital trigger because it is input through a PFI line or the RTSI bus. See the following example for more information:
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B89AB47E46F66897E034080020E74861&p_node=175383&p_source=external

[Roberto_N.]

Many thanks,
that's very useful.