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C-5
External Clocking
Some applications require that the timing, or pacing, of data-acquisition
sampling be synchronized to an external clock signal. To do this with the
DAS-8, you must connect the external clock to the INTERRUPT INPUT
[24] input on the external analog D-connector on the board’s mounting
bracket. To inform DriverLINX that external clocking is requested, use
either a Rate Timing Event on Logical Channel 6 with external clock
input or a Digital Timing Event that specifies “Ext Clock” as the digital
mask, zero as the pattern, and “not equals” as the test. External clocking
can be used in either polled or interrupt modes.
Data Coding
The A/D uses offset binary coding for bipolar inputs and straight binary
for unipolar inputs. For all ranges and configurations the minimum value
reported is 0 and the maximum value is 4095.
A/D data can be returned in native or integer formats. The native format
of the DAS-8 returns the 12A/D bits left shifted by four bits and the
low-order four bits are zero. The integer format returns the data as a
two’s-complement number with a range of 2048 to 2047 in bipolar mode
and 0 to 4095 in unipolar mode. Integer format is only supported for
polled and interrupt modes, while native format is supported by all
modes.
For example, for a gain of 1 in the ±10V range (bipolar configuration) the
voltage resolution would be
.
Table C-3.
Input Voltage
A/D Binary Value
-10V
0
0V
2048
+4.88mV
2049
+10V
4095
20V
4096
------------
4.88
=
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