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Analog Input Features
2-15
Data Conversion Modes
DAS-1800ST/HR Series boards support three modes of data conversion:
paced, burst, and burst with SSH. The data conversion modes are
described as follows:
●
Paced mode
— Paced mode is best-suited for continuous scanning of
channels at a constant rate. In the paced mode, the conversion rate
equals the pacer clock rate. The sample rate, which is the rate at
which a single channel is sampled, is the pacer clock rate divided by
the number of channels you are sampling.
●
Burst mode
— In burst mode, each pulse from the pacer clock starts
a scan of channels. The conversion rate equals the rate of the burst
mode conversion clock. The sample rate, which is the rate at which a
single channel is sampled, equals the pacer clock rate.
The sample rate (pacer clock rate) should be no more than the burst
mode conversion clock rate divided by the number of channels in the
burst. The maximum burst mode conversion clock rate is
gain-sensitive, as explained in “Maximum Achievable Throughput
Rates” on page 2-9.
●
Burst mode with SSH
— In burst mode with SSH, each pulse from
the pacer clock starts a simultaneous scan of all channels. The
conversion rate equals the rate of the burst mode conversion clock.
The sample rate, which is the rate at which a single channel is
sampled, equals the pacer clock rate.
One extra tick of the burst mode conversion clock is required to
sample and hold the values. Therefore, the sample rate (pacer clock
rate) can be no more than the burst mode conversion rate divided by
the sum of one plus the number of channels in the burst.
You cannot use burst mode with SSH for a DAS-1800HR Series
board.
For information on the signal interface between a DAS-1800ST
Series board and SSH hardware, refer to “Using Digital Control
Signal SSHO” on page 2-26.
Figure 2-4 shows the timing relationships of the data conversion modes
for a scan of channel 4 to channel 7.
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