USB-2533 User's Guide
Functional Details
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3.
Bring the analog input signal toward the desired threshold. When the input signal is at the threshold
(± some tolerance) the sweep will be triggered.
4.
Before re-arming the trigger, again move the analog input signal to a level that is more than 2.5% of the
full-scale range
away from
the desired threshold.
For example, if you are using the ±2 V full-scale range (gain = 5), and you want to trigger at +1 V on the rising
edge, set the analog input voltage to a start value that is less than +0.9 V (1 V – (2 V * 2 * 2.5%)).
Digital triggering
A separate digital trigger input line is provided (TTL TRG), allowing TTL-level triggering with latencies
guaranteed to be less than 1 µs. You can program both of the logic levels (1 or 0) and the rising or falling edge
for the discrete digital trigger input.
Software-based triggering
The three software-based trigger modes differ from hardware analog triggering and digital triggering because
the readings—analog, digital, or counter—are checked by the PC in order to detect the trigger event.
Analog triggering
You can select any analog channel as the trigger channel. You can program the trigger level, the rising or falling
edge, and hysteresis.
Pattern triggering
You can select any scanned digital input channel pattern to trigger an acquisition, including the ability to mask
or ignore specific bits.
Counter triggering
You can program triggering to occur when one of the counters meets or exceeds a set value, or is within a range
of values. You can program any of the included counter channels as the trigger source.
Software-based triggering usually results in long period of inactivity between the trigger condition being
detected and the data being acquired. However, the USB-2533 avoids this situation by using pre-trigger data.
When software-based-triggering is used, and the PC detects the trigger condition—which may be thousands of
readings after the actual occurrence of the signal—the USB-2533 driver automatically looks back to the
location in memory where the actual trigger-causing measurement occurred, and presents the acquired data that
begins at the point where the trigger-causing measurement occurs. The maximum inactive period in this mode
equals one scan period.
Stop trigger modes
You can use any of the software trigger modes explained previously to stop an acquisition.
For example, you can program an acquisition to begin on one event—such as a voltage level—and then stop on
another event—such as a digital pattern.
Summary of Contents for USB-2533
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