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Chapter 4 Arb Operation
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National Instruments Corporation 4-9 DAQArb 5411 User Manual
The DAQArb 5411 uses a 32-bit, high-speed accumulator with a lookup
memory and a 12-bit DAC for DDS-based waveform generation.
Figure 4-7 shows the building blocks for DDS-based waveform
generation.
Figure 4-7. DDS Building Blocks
The lookup memory is dedicated to the DDS mode only and cannot be
used in Arb mode. You can store one cycle of a repetitive
waveform—a sine wave, a triangular wave, a square wave, or an
arbitrary wave—in the lookup memory. Then, you can change the
frequency of that waveform by sending just one instruction. You can
use DDS mode for very fine frequency resolution function generation.
You can generate sine waves of up to 16 MHz with a frequency
resolution of 10.0 mHz. Because this mode uses an accumulator,
waveform generation loops back to the beginning of the lookup memory
after passing through the end of the lookup memory.
You should use DDS mode for standard function generation rather than
for arbitrary waveform generation.
In this mode, each stage is made up of two instructions: the frequency,
which specifies the frequency of the waveform to be generated, and
time, which specifies the time for which the frequency has to be
generated.
80 MHz Oscillator
Div/2
16-Bit
Counter
Sequencer
Instruction FIFO
Frequency
Time
Data Out (16)
DDS
Time
Frequency
Lookup
Memory
(14)