Chapter 2 Function Reference — Configure_HW_Analog_Trigger
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National Instruments Corporation 2-87 NI-DAQ FRM for PC Compatibles
If you set trigSource to ND_THE_AI_CHANNEL, you can use the signal connected to one of
the analog input pins for triggering. In this case, the signal is amplified on the device before
it is used for trigger generation. You can use this source selection under the following
conditions:
• Y ou want to perform data acqu isition from a sing le analog input channel (t he DAQ family
of functions). You only can use the channel you are acquiring from for analog triggering.
• You want to perform data acquisition from more than one analog input channel
(aco m bination of the DAQ and SCAN families of functions). The only analog input
channel you can use as the start trigger is the first channel from your list of channels. You
cannot use this form of the analog trigger for the stop trigger in case of pretriggered data
acquisition.
Note The PCI-6110E and PCI-6111E can use any analog input channel.
• You do not want to perform any analog input operations (the AI, DAQ, and SCAN families
of functions). You must use AI_Setup to select the analog input channel you want to use
and the gain of the instrumentation amplifier. You also can use AI_Configure to alter
the configuration of the analog input channel.
• You want to use AI_Check, and you want to use the analog trigger for conver sion timing.
You do not have to perform any special steps.
The reason for using these constraints is that if you are scanning among several analog input
channels, signals from those channels are multiplexed in time, and the analog triggering
circuitry is unable to distinguish between signals from individual channels in this case.
For DSA devices only, any of the analog input channels can be the source of the analog
trigger, even channels that are not part of the channel list set in DAQ_Start or SCAN_Setup.
Set trigSource to the channel number of the channel to monitor for the analog trigger.
Using This Function
When you use this function, you activate the onboard analog triggering hardware.
Thisonboard hardware generates a digital trigger that the DAQ-STC then uses for timing and
control. To use the analog trigger, you need to use this function and the Select_Signal
function. To use analog triggering, use as much hysteresis as your application allows because
the circuitry used for this purpose is verynoise-sensitive.
For E series devices, when you use Select_Signal, set source to ND_PFI_0 for your
signal, and set sourceSpec as appropriate. Notice that the two polarity selections give you
timing control in addition to the five triggering modes listed here. For DSA devices, when you
use Select_Signal, set source to ND_ATC_OUT for your signal, and set sourceSpec to
ND_DONT_CARE. NI-DAQ will route the analog trigger circuit output as appropriate for the
device.