Data Translation DT9871, User Manual

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Chapter 6
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Conversion Modes
TEMPpoint, VOLTpoint, and MEASURpoint instruments support continuous scan conversion
modes for reading input measurements.
Continuous scan mode takes full advantage of the capabilities of the TEMPpoint, VOLTpoint,
and MEASURpoint instruments. Use continuous scan mode if you want to accurately control
the period between successive simultaneous conversions of specific channels.
In addition to the analog input channels, this conversion mode allows you to read the digital
input port (all 8 digital input lines) as part of the analog input data stream. This feature is
particularly useful when you want to correlate the timing of analog and digital events.
Specifying Analog Input Channels
Using software, enable the analog input channels that you want to sample by specifying the
channel numbers in the channel list. You can also read the value of the digital input port
through the analog input data stream by specifying the digital input channel in the channel
list; the number of the digital input channel depends on how many channels the TEMPpoint,
VOLTpoint, or MEASURpoint instrument provides, as shown in
Table 5 .
The channels are read in order from the lowest channel number to the highest channel number
in the list of enabled channels; this process is known as a scan.
How Continuous Scan Works
When you issue a command to start the scan, the instrument simultaneously samples all the
analog input channels, CJC inputs (if applicable), and the digital input port, and converts the
analog inputs to temperature, resistance, or voltage based on the sensor type. If the channel is
enabled, the sampled data is placed in the FIFO on the instrument.
Table 5: Supported Channels for Continuous Operations
Total Number of
Analog Input Channels
Channel for Reading
the Digital Input Port
0 to 7 8
0 to 15 16
0 to 23 24
0 to 31 32
0 to 39 40
0 to 47 48