Analog Output >> General Properties >> DAC >> Reference Voltage >> External Source

NI-DAQmx C Properties

Analog Output >> General Properties >> DAC >> Reference Voltage >> External Source

Data Type: char*
Description: Specifies the source of the DAC reference voltage if Source is DAQmx_Val_External. The valid sources for this signal vary by device.

You can get/set/reset this property using:
  DAQmxGetAODACRefExtSrc
  DAQmxSetAODACRefExtSrc
  DAQmxResetAODACRefExtSrc