Measurement Computing Data Translation DT3010 Series, Руководство пользователя, Страница: 111 / 232

Chapter 6
110
Note: The DT3010-268 board only provides an External A/D Trigger and Clock Enable
signal. This signal is pulled high on the DT3010-268 board by a 22 k
Ω
resistor. You can use
this signal to enable or disable the external digital trigger and the external A/D sample clock.
A high signal enables both the external digital trigger and the external A/D sample clock,
while a low signal disables both the external digital trigger and the external A/D sample
clock.
Analog Input Conversion Modes
DT3010 Series boards support the following conversion modes:
• Single-value operations are the simplest to use but offer the least flexibility and efficiency.
Use software to specify the range, gain, and analog input channel (among other
parameters); acquire the data from that channel; and convert the result. The data is
returned immediately. For a single-value operation, you cannot specify a clock source,
trigger source, trigger acquisition mode, scan mode, or buffer.
Single-value operations stop automatically when finished; you cannot stop a single-value
operation.
• Scan mode takes full advantage of the capabilities of the DT3010 Series boards. In a scan,
you can specify a channel list, clock source, trigger source, trigger acquisition mode, scan
mode, and buffer. Two scan modes are supported: continuously-paced scan mode and
triggered scan mode (often called burst mode). These modes are described in the
following subsections.
Using software, you can stop a scan mode operation by performing either an orderly stop
or an abrupt stop. In an orderly stop, the board finishes acquiring the specified number of
samples, stops all subsequent acquisition, and transfers the acquired data to host memory;
all subsequent triggers or retriggers are ignored. In an abrupt stop, the board stops
acquiring samples immediately; the acquired data is not transferred to host memory, but
all subsequent triggers or retriggers are ignored.
Continuously-Paced Scan Mode
Use continuously-paced scan mode if you want to accurately control the period between
conversions of individual channels in a scan.
When it detects an initial trigger, the board cycles through the channel list, acquiring and
converting the value for each entry in the channel list; this process is defined as the scan. The
board then wraps to the start of the channel list and repeats the process continuously until
either the allocated buffers are filled or you stop the operation. Refer to
page 119 for more
information on buffers.
The conversion rate is determined by the frequency of the A/D sample clock; refer to page 108
for more information on the A/D sample clock. The sample rate, which is the rate at which a
single entry in the channel list is sampled, is determined by the frequency of the A/D sample
clock divided by the number of entries in the channel list.