1. DescriptionIf a device supports analog hardware triggering, there is an internal signal, known as the analog trigger circuitry output (ATCOUT), that is high whenever the signal on the trigger channel meets the specified trigger conditions. This signal can be routed to either the counter source or gate pins to control it. The signal can also be routed to other locations, like PFI or RTSI lines. ATCOUT can also be used to trigger an analog output operation.
See the Analog Trigger link at the bottom of this page for more information on the types of analog triggering available.
One particularly useful application is measuring the frequency of an analog signal using hardware. The analog trigger can be set to trigger every time that the analog signal is above (or below) a certain voltage that is reached once per waveform period. ATCOUT then pulses once per period. One counter can be used to produce a gate signal of a known width (which is fed to the gate of the second counter), and the second counter can count ATCOUT on its source pin. The frequency of the signal will be counter_value / time_gate_is_high.
2. Common Applications
Using the ATCOUT signal only works on devices that peform hardware analog triggering one channel at a time.
The analog trigger can be configured using AI Trigger Config VI with "type" = "general purpose analog trigger ATCOUT," "trigger source" = appropriate channel (recommend "PFI0"), and "level" and "additional trigger specification" set to the appropriate values. This VI configures the trigger without starting an analog input acquisition. (Starting one will unconfigure the trigger.) To route the trigger to a counter, use the Counter Set Attribute VI with "attribute ID" = "gate selection" (2) or "attribute ID" = "source selection" (1), "attribute value type" = "PFI n" (36), and "attribute value number" = 7.
Configure the analog trigger with Configure_HW_Analog_Trigger. Call GPCTR_Change_Parameter to route ATCOUT to a counter with paramID = ND_GATE or paramID = ND_SOURCE and paramValue = ND_PFI_0.
How to Use the Analog Trigger Circuitry Output as an External Signal
Measuring Frequency of a Periodic Analog Signal Using Counters and Hardware Analog Triggers