Help: Can you use software trigger on a digital line.

Question

Hi:
We have a legacy DAQCARDard 700 which does not support hardware triggering.
We have a trigger from our instrument that is 5 V+ and we would like to
trigger when it drops to 0 V. We have several questions.
1. Do we need to invert the signal in MAX or is that only for V that are
negative?
2. Is there a good example in the examples where the state of this digital
line is used to trigger an analog acquisition? When we tried using the
digital trigger examples, we had an error saying that the hardware did not
support that mode.
3. We have an analog software trigger mode (based on the Analog Software
Trigger example) working which we would like to modify over to read the
digital line, but we have done very little wi
th digital I/O.
4. The digital trigger has been assigned a virtual channel of dtrg.
Any help would be much appreciated.
Thanks in advance,
Pete

Answer 1

Thanks Doug,
If we read the digital line instead of as an analog line would it improve
the accuracy of the triggering. Everything works now except we have a
little bit of timing jitter within about 1 data point scanning at 50 kHz.
However, I've never done any digital i/o with LabView, but may I should work
through some of the tutorials. If you thought that this might solve the
jitter problem. Would checking the state of the digital line allow a faster
response with softtrig, I guess is my question?
Pete
"Doug Norman" wrote in message
news:[email protected]..
> Hello Pete,
>
> You are correct that the DAQCard-700 has no digital (or analog)
> hardware trigger. The analog trigger example t
hat is working for you
> is using conditional retrieval. This is where data is always being
> acquired and the driver looks at the values to determine when to
> "trigger" and read the data into LabVIEW. To answer your questions:
> 1. I don't think you need to invert the signal. This is for when you
> want a digital low (below 0.8 volts) to show up as a digital high, and
> a high (above 2.0 volts) to be read as a low.
> 2. I don't know of a good example. You would basically have to
> monitor the digital line. When it goes from high to low you would
> then start your analog acquisition.
> 3. I think this could be your best bet. If you have enough analog
> input lines, why not just connect this digital signal as one of your
> analog inputs. Then use this example to trigger when the 5 volts
> drops to 0. It won't hurt to acquire your digital signal on an anlog
> input along with your other data.
> 4. I don't understand this question.
>
> Best Regards,
>
> Doug Norman