Not getting any signal out from the NI9472 cRIO

Question

I want to generate PWM signal from the NI9472 in cRIO.
I made a vi which (I think) should generate the pulse in the DO0 port.
but when I measure DO0 with oscilloscope, I get nothing out from it.  (The LED comes up in NI9472 that channel 0 is active)
Is there anything I am doing wrong here? (I attached the project and block diagram in jpg)
Thank you so much.
Attachments:
PWM.zip ‏100 KB
121.jpg ‏54 KB

Answer 1

Hi hinewwiner,
Overall, your implementation looks good. I think it might be worth your while
to look at two other examples of PWM I found on our website which may be more
efficient and more accurate. Another important thing to not about the 9472 is
that it must have an external power supply connected to it for any output to occur.
If you do not have any supply, the channel may be switching (and thus the
channel LED will show activity,) but you will not see any change in output
voltage. Also note that the LED should be off when the channel is not switched,
and on when it is switched. So if you run your PWM at a slow enough speed, you
will see the light turn on when the pulse is high and off when the pulse is low
(at the rates shown in your attached project, your eye will probably not be
able to discern a change.) It may also be helpful for you to describe exactly
what the LED is doing to get a better idea of whether the code has stopped in a
channel closed position, or if it is simply changing very fast.
Another slight possibility is that the unit has experienced an over current
condition. Because the module has automatic over current protection, if it is
exposed to a current greater then 13A, the unit will open the channel switch
and wait for a reset. This may have occurred, and the activity light will still
show normal operation. To ensure that this condition is removed, simply reset
the channel, or disconnect and reconnect the external power supply.
For testing purposes, it may also make sense to simplify your VI by removing
the case structure, start button, stop button and outside while loop. You can
then simply start the VI in your real time controller, and stop the VI using
the abort command given in your real time code.
Here are two great resources for creating PWM functions in FPGA.
Developing a PWM Interface using LabVIEW FPGA
Pulse Width Modulation Example DAQ Personality
Sincerely,
Asa Kirby
Applications Engineer
National Instruments
Message Edited by Asa_K on 05-20-2008 12:22 PM
Asa Kirby
CompactRIO Product Marketing Manager
Sail Fast!