Can I Use a Clock Signal From My USB Device As The Source For My Timed Loop? Hardware: Multifunction DAQ (MIO)
Problem: I would like to use a clock signal from my USB device as the source for my timed loop. I know that there are several timebases that are faster and/or more accurate than my computers 1kHz clock. When I specify the device as my source, I get an error saying this is not supported by my device. It will work for my PXI or PCI form factor of the device. Solution: The reason that your device does not support being used as a source for your timed loop is due to the fact that the USB bus causes a lot of jitter/latency in your signals. This is taken care of for things like data transfer, etc., however when you try to provide your software loop with a hardware clock, you must pass that clock through the bus. This can be done with the PCI and PXI buses, but the USB bus is not reliable enough to make this useful. What all this means is that you cannot use any clock on your hardware to run your timed loop. Most computers have a 1kHz clock on it to control timing of the computer. This is why you can use that rate in your timed loop. The 1MHz option (which should be greyed out for non-real time systems) is for real time operating systems which have an onboard clock which runs this fast. Since all of this uses hardware oscillators, software cannot be used to provide this clock. Depending on your application, you may be able to use the timing VI's (for example our Time Elapsed VI) to help control the timing. Related Links: Developer Zone Tutorial: Overview: USB For Measurement And Automation Developer Zone Tutorial: USB Data Acquisition Frequently Asked Questions (FAQ) Attachments:
Report Date: 03/31/2008 Last Updated: 04/14/2008 Document ID: 4JUG714C |
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