ADLINK Technology USB-1901, Руководство пользователя

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Operation 55
USB-1900 Series
An onboard data FIFO buffers the waveform patterns for wave-
form generation. If the size of a single waveform is less than
that of the FIFO, after initially loading the data from the host
computer’s memory, the data in FIFO can be reused when a
single waveform generation is completed and will not subse-
quently occupy USB bandwidth.
However, if the size of a single waveform exceeds that of the
FIFO, it must be intermittently loaded from the host computer’s
memory via USB peripheral controller, and will occupy USB band-
width.
If the value specified in the UC_counter is less than the sample
size of the waveform patterns, the waveform is generated incre-
mentally. For example, if a 16-sample sine wave is defined and the
UC_counter set to 2, the generated waveform will be a 1/8-cycle
sine wave for every waveform period, and a complete sine wave
generated for every 8-iterations. If a UC_counter value is specified
that exceeds the sample size of the waveform LUT (for example,
32), the generated waveform will be a 2-cycle sine wave for every
waveform period.
Figure 4-17: Infinite Iteration Waveform Generation
UC_Counter = 4
4 update count, iterate infinite
(UC_counter = 4, IC_counter = infinite, DLY2_counter = 0)
Trigger
DAWR
WF_in_Prog
Wave
Single waveform