Free Trial

Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.

  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL
Help

Chapter 2. Signals and DAQ > Keeping Time with DMA and FIFO

2.4. Keeping Time with DMA and FIFO

Whether you are doing analog input or output, or digital I/O, there are times you’ll need to sample data or generate data at a very consistent rate. For instance, if you’re acquiring an analog input waveform for frequency analysis, you need your samples to be evenly spaced in time. DMA (Direct Memory Access) and FIFO (first-in, first-out) buffers are two hardware mechanisms that make this possible. Both mechanisms buffer DAQ data into high-speed memory before the computer processes it so that no real-time data is lost. FIFO’s memory resides on the DAQ device, but DMA uses your computer’s normal memory.

For example, suppose we have a perfectly timed system, and we sample a 2 Hz sine wave at 100 Hz for one second. Figure 2-21 shows the perfect 2 Hz sine wave, superimposed on the locations of the 100 Hz samples.


  

You are currently reading a PREVIEW of this book.

                                                                                                                    

Get instant access to over $1 million worth of books and videos.

  

Start a Free 10-Day Trial


  
  • Safari Books Online
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint