1. First of them, I am currently
using your suggestion of arrays to construct my signals. But I had
encountered a problem. I have generated 6 different signals using array
and output from DIO 0 to DIO 5. I notice that the signals coming out
of DIO 1 to DIO5 is unstable when I viewed it in oscilloscope. Only DIO
0 has a stable signal. Therefore, I elimilated the possibility of wrong
settings on my oscilloscope that might cause the displaying of unstable
signals. Can you recommend or attach an example on how to use array to
generate signals? I might just have done it wrongly after all. I have
attached my VI for your referrance.
When you say unstable I'm not sure what that means. You've got a pattern that's approximately 20us long (1/(2MHz) * ~40 samples). You're repeating that pattern forever. There's nothing there for a scope to trigger on to show you your pattern. My recommendation to see your pattern clearly on a scope is to adjust your script like so:
script myScript1
Repeat forever
Generate wave1 marker0(0)
end repeat
end script
This will cause a marker to be output on the first sample of your waveform each time it's repeated. You can use the niHSDIO Export Signal.vi to route that marker to a PFI line. If you use your scope to trigger on the marker, you should be able to see your pattern the way you expect.
2. I found is that for DIO 0, the voltage level is always higher than the rest of the channels. Why is that so? I am using NI-PXI-6552
That's not expected. The output lines are sourced from a common supply. I noticed that you are not explicitly setting the voltage output levels in your VI. So I would do two things - first, add the niHSDIO Configure Voltage.vi to your VI and explicitly set the output levels you want (VOL and VOH). Second, make sure that the input impedance on your scope is set to the same for all of the channels. Most scopes have an option for 1Mohm (or 10Mohm) and for 50ohms. Make sure all your channels are set the same.
3. For my project, I will need to firstly generate 6
signals to pump to my IC chips and then accquire 1 signal from the chip
and finally generate another signal back to the chip. Will I be able to
do this using one card? Or is it that for PXI-6552, we can only generate signals simultaneous?
Acquisition and generation on the PXI-6552 can run simultaneously. Do you know the expected result from your chip? If so, you can use one of our advanced features - Hardware Compare - to functionally test and determine if the expected result is correct all from the 6552, which will decrease your test time per item.
If you are doing data collection or validation of a range of data, that's also possible. If you look at the examples provided in with NI-HSDIO, you'll see that there is a library of examples for doing simultaneous generation and acquisition.
The PXI-6552 can even use a pin for both acquisition and generation at the same time, allowing bidirectional pins to be tested.
4. Lastly, I would like to clarify my understanding of my card NI-PXI-6552. In order to generate a certain signal for channel, I will need to enter the data in binary format?
For
example : Binary format : 1 0 1 1 means channel 0,1 and
3 will get logic '1', while channel 2 will get logic '0' ?
You are correct. Using a binary representation for a U32 (32-bit unsigned integer) goes from MSB (bit 31) to LSB (bit 0) left-to-right on your screen. The PXI-6552 also supports Labview's waveform data type and 'HWS' which is a waveform generated by our digital waveform editor.
For a U32 and the PXI-6552, here's how it breaks down:
31 19 16 15 0
XXXX XXXX XXXX 0000 0000 0000 0000 0000
Since the 6552 only has 20 channels, bits 20-31 are ignored. Each bit is assigned to the channel number of the same value (bit 0 is assigned to channel 0). Only channels that are specified in your channel list for niHSDIO Assign Dynamic Channels.vi are activated for a given generation session.
I hope that helps. Please feel free to ask more questions. I'm attaching your VI with the modifications I recommended.
Keith Shapiro
National Instruments R&D
