Analog Input Subsystem
C-9
Internal Clocking
Specify internal clocking using a Rate Timing Event as a rate generator
(RATEGEN) on Logical Channel 0 with an internal source. For hardware
independence, the application may specify the clock channel using the
symbolic constant, DEFAULTTIMER, which always uses the Logical
Channel assigned by hardware for analog input. With a 5MHz master
clock, each tic is 200 ns.
Burst Mode Sampling
All DAS-1800 boards support burst mode sampling. To setup burst mode
sampling, specify the
mode
field of a Rate Event as BURSTGEN. The
period
field is the time in clock tics between bursts. The
onCount
field is
the time in clock tics between successive samples within a burst, and
pulses
specifies the number of samples in a burst. The number of pulses in
a burst must equal the number of channels scanned in the burst.
POLLED
,
INTERRUPT
, and
DMA
modes can support burst mode sampling, but
exceeding the maximum sustainable acquisition rate in each mode will
cause loss of data. Also, the duration specified in the
onCount
field must
be within the range of 6µs (30 tics) minimum (20µs for DAS-1800HR) to
64µs (320 tics) maximum.
Repeat Mode Sampling
The DAS-1802HR-DA provides an option to sample the same channel 1
to 4095 times before advancing to the next channel in the channel/gain
queue. To setup repeat mode sampling, choose a rate or burst timing event
as described above. Bit-wise OR the
pulses
field with
PULSE_REPEAT_COUNT_FLAG to set the MSB. Specify the number
of pulses in each burst in the low-order word of the
pulses
field by using a
bit-wise AND with PULSE_COUNT_MASK. Specify the repeat count in
the high-order word by using a bit-wise AND with
PULSE_REPEAT_COUNT_MASK.
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