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TECHNICAL Notes |
Introduction Technical and support topics are addressed in this section, as are application ideas. |
3. Data Acquisition with the Model AVR-32 or Model BVR-32Data Acquisition consists of the Record and Playback
functions, which are defined as follows:
These performance figures should serve only as a guide. |
4. Pulse Generation with the Model AVR-32 or Model BVR-32The D/A converter or TTL output on the AVR/BVR series boards may serve as outputs in pulse (or more complex waveform) generator applications. As with many applications using the AVR/BVR series boards, system designers can choose the engine mix driving the application: DSP or FPGA, or, as is very often the case, some combination of the two. In the pulse generation example, the output will be clocked by an available clock, usually generated by the onboard DDS (Direct Digital Synthesizer) The software used in the DSP approach will look familiar to those who have already programmed DSPs or even general purpose CPUs. One can expect a maximum output rate of 3 MHz (resolution of 333 ns). The onboard FPGA is ideal for this kind of high speed, repetitive task. Use the programmable DDS, or the fixed 60 MHz clock, which would provide a resolution of 17 ns. With a 17 ns resolution and 40 bit counter, easily implemented in even the smallest FPGA, a pulse pattern may be implemented on a very long period. The design entry for this application is most easily done using the VHDL or Verilog languages. The source code will look reassuringly familiar to C programmers of DSPs and CPUs. Most importantly, performance will be increased by a factor of 20. The DSP is free for other functions, such as modulation or frequency shifting tasks. |
5. MODA 2 Data Acquisition Software: Progress ReportMODA 2 is the data acquisition program for the Model AVR/BVR series boards. It is unique in one major respect: the data collection is done on a dedicated 'private' disk connected to the AVR/BVR board's 50 pin connector via a ribbon cable. The advantages of this approach are 1) the higher maximum speed, measured in samples/sec. at which data may be collected and 2) the data collection process does not clash with the Windows OS (or other OS), or other applications, for system resources. How it works A task file is created by the user, either by using a text editor or the task file editor. The task file specifies the function to be performed by MODA 2, as well as the parameters necessary to support that function. Example Here we are recording to private disk. Sectors 2 through 99711 on the private disk will be written to at the rate of 1 MSample/sec. Each sector holds 256 16 bit words. The signal source is the BINP analog input channel on the Model BVR-32. Since 2 hard drives may be connected to the AVR/BVR board, we have to specify that too. In this case we are using the first hard drive (harddrive = 0). The taskfile generator simplifies data entry and
checks for errors. As you can see, it allows for file
length entry in units of time or number of samples to be
collected, which are more intuitive units than 'sectors'.
The playback and copy_public_to_private functions operate in similar fashion. At this time, MODA 2 and the task file generator are available in a preliminary version which has the following limitations: Record and Playback speeds limited to 1 MSample/sec. (2 MBytes/sec.) Single channel operation only. |