Data Translation DT9800 Series, User Manual

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Principles of Operation
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A/D Sample Clock Sources
The DT9800 Series function modules allow you to use one of two
clock sources for pacing analog input operations in continuous mode:
• The internal A/D sample clock, which uses the 24-bit A/D
Counter on the module, or
• An external A/D sample clock, which you can connect to the
screw terminal panel.
You use an A/D sample clock to pace the acquisition of each channel
in the channel-gain list; this clock is also called the A/D pacer clock.
Note: If you enter digital input channel 16 in the channel-gain list,
the A/D sample clock (internal or external) also paces the
acquisition of the eight digital input lines.
The following subsections describe the internal and external A/D
sample clocks in more detail.
Internal A/D Sample Clock
The internal A/D sample clock uses a 12 MHz time base.
Conversions start on the rising edge of the counter output; the output
pulse is active low.
Using software, specify the clock source as internal and the clock
frequency at which to pace the operation. The minimum frequency
supported is 0.75 Hz (0.75 Samples/s); the maximum frequency
supported depends on the module type.
Table 4 lists the maximum
sampling rate of the DT9800 Series function modules.