National Instruments 5411 - Manual (Page 36)

Chapter 4 Arb Operation
© National Instruments Corporation 4-11 DAQArb 5411 User Manual
If you want to update every next sample in lookup memory at an
integral subdivision, D, of the maximum clock rate, you should write an
FCW value of 2
(N-L-D+1)
. In other words, for an effective update rate of
every sample at half the maximum clock rate, you should write an FCW
value of 2
(32-14-2+1)
, which equals 131,072.
Frequency Hopping and Sweeping
You can define a staging list in DDS mode for performing frequency
hops and sweeps. The entire staging list uses the same buffer loaded
into the lookup memory. All stages differ in the frequency to be
generated. As shown in Figure 4-7, a stage in DDS mode has a different
instruction set than Arb mode.
Note: The minimum time that a frequency should be generated is at least 2 µs.
Therefore, the maximum hop rate from one frequency to the other
frequency is limited to 500 kHz.
Note: The maximum number of stages that can be stored in the instruction FIFO
for DDS mode is equal to 340. For more information on the waveform
generation process, refer to your software manuals.
Triggering
Triggering is a feature by which you can start and step through a
waveform generation. The trigger sources and trigger modes are
explained in the sections below.
Trigger Sources
Trigger sources are software selectable. By default, the software
provides the triggers. You can use also use an external trigger from a
pin on the digital I/O connector or from any of the RTSI trigger lines on
the RTSI bus. Figure 4-8 shows the trigger sources for the
DAQArb 5411.