Measurement Computing USB-1602HS-2AO - Manual (Page 20)

USB-1602HS-2AO User's Guide Functional Details
20
Triggering
Triggering can be the most critical aspect of a data acquisition application. A trigger event occurs and data
acquisition begins when specified conditions are met. You select the trigger mode and set up its parameters with
software.
The USB-1602HS-2AO supports both hardware-based and software-based triggers. With a hardware-based
trigger, an output value is compared in hardware to an input level on a specified channel. With software-based
triggers, the analog, digital, and/or counter readings are checked by the PC in order to detect the trigger event.
The USB-1602HS-2AO supports the following trigger sources:
 Hardware-based triggers:
o Analog input hardware
o External digital trigger input
 Software-based triggers:
o Analog software trigger
o Digital pattern
o Counter/totalizer
Hardware-based triggering
With a hardware-based trigger, an output value is compared in hardware to an input level on a specified
channel.
Analog input hardware
In this mode, the acquisition is triggered when a specified input level is achieved. The USB-1602HS-2AO uses
true analog triggering in which the trigger level you program sets an analog DAC, which is then compared in
hardware to the analog input level on the selected channel. This ensures an analog trigger latency that is less
than 1.5 µs.
You can select any analog channel as the trigger channel, but the selected channel must be the first channel in
the scan. You can program the trigger level, the rising or falling edge, and hysteresis level. The trigger level can
be any value within the voltage range for the selected trigger channel.
External digital trigger input
A separate digital trigger input line ( DIG TRIG ) allows TTL-level triggering with latencies guaranteed to be no
less than 100 nS. The acquisition is triggered when a rising or falling edge is detected .
The trigger level is set at TTL sensitive. Latency is one sample period, maximum. The input signal range is
±15 V. The trigger edge, logic level (1 or 0), and the rising or falling edge for the discrete trigger input are
software selectable.
Software-based triggering
The three software-based trigger modes differ from hardware analog triggering and digital triggering because
the analog, digital, or counter readings are checked by the PC in order to detect the trigger event.
Analog software
The acquisition is triggered when the computer issues a software command. You can select any analog channel
in the scan as the trigger channel. The trigger level, the rising or falling edge, and hysteresis are software
programmable. The trigger level can be any value within the range of the trigger channel. Latency is one sample
period, maximum.
Digital pattern
The acquisition is triggered with a digital input channel pattern. You can select any scanned digital input
channel pattern to trigger an acquisition, including the ability to mask or ignore specific bits.
You can program to trigger the conversion when equal to, not equal to, above, or below a value. Latency is one
sample period, maximum.