National Instruments 5411 - Manual (Page 27)

Chapter 4 Arb Operation
DAQArb 5411 User Manual 4-2 © National Instruments Corporation
functions such as arbitrating the data buses and controlling the triggers,
filters, attenuators, clocks, PLL, RTSI switch, instruction FIFO, and
direct digital synthesizer (DDS). The memory controller controls the
waveform memory on the memory module. The data from the memory
is fed to a digital to analog converter (DAC) through a half-band
interpolating digital filter. The output from the DAC goes through the
filter, amplifiers, attenuators and, finally, to the I/O connector.
Waveform Generation
The DAQArb 5411 can generate waveforms in two modes: Arb and
DDS. Use Arb mode for any arbitrary waveform generation, but you can
use DDS mode for standard frequency generation such as sine, TTL,
square, and triangular waveforms.
In Arb mode, you can define waveforms as multiple buffers. You can
link and loop these buffers in any order you desire. This mode has more
features and is more flexible than DDS mode.
Note: If you use Virtual Bench software, you must use VirtualBench-Arb for Arb
mode.
DDS mode is more suitable for generating standard waveforms that are
repetitive in nature, for example, sine, TTL, square, and triangular
waveforms. In DDS mode, you are limited to one buffer, and the buffer
size must be exactly equal to 16,384 samples.
Note: If you use VirtualBench software, you must use VirtualBench-Function
Generator for DDS mode.
Figure 4-2 shows a block diagram representation of the data path for
waveform generation. The data for waveform generation can come from
either the waveform memory module or DDS lookup memory,
depending on the mode of waveform generation. This data is
interpolated by a half-band digital filter and then fed to a high-speed
DAC. The data has a pipeline delay of 26 update clocks through this
digital filter.