Chapter 10
Miscellaneous Functions
©
National Instruments Corporation
10-3
DAQ-STC Technical Reference Manual
10.4 Frequency Output
The frequency output pin FOUT provides a divide-down version of the master timebase for
board use. FOUT can output FOUT_TIMEBASE divided by 1 through 16.
The duty cycle is equal to 50% when the divider setting is 1 or an even number. When the
divider is set to an odd number (except 1), the duty cycle is less than 50%. The duty cycle is
determined with the following equation duty cycle = N/D, where D = the divider setting and
N = (D-1)/2. In other words, the output will be high for N time base clocks and low for N+1
timebase clocks.
10.5 Analog Trigger
The analog trigger circuit provides a method of triggering the analog input, analog output,
or general-purpose counter/timer operation based on the significant instances of an analog
waveform. Two voltage references, LOW and HI, are typically available for comparison.
External to the DAQ-STC, a comparator tests the analog waveform and generates a digital
value indicating whether the analog waveform is below the LOW value or above the HI value.
The low-indication and high-indication signals from the comparator are connected directly to
the ANALOG_TRIG_IN_LO and ANALOG_TRIG_IN_HI pins, respectively.
When the analog trigger circuit is enabled, the analog trigger signal takes over the PFI0 slot
in the PFI input selectors. In this case, the PFI0/AI_START1 pin can no longer be an input,
although it can still output the analog input START1 signal.
Many boards will also have the ability to source an analog trigger to external devices based
on DAQ-STC timing. The output ANALOG_TRIG_DRIVE selects the I/O direction of the
analog trigger signal. You have direct control over ANALOG_TRIG_DRIVE through a bit in
the register map.
AI_OUT_TIMEBASE
AI_Output_Divide_By_2
1, 2
AO_IN_TIMEBASE1
AO_Source_Divide_By_2
1, 2
AO_OUT_TIMEBASE
AO_Output_Divide_By_2
1, 2
G_IN_TIMEBASE1
G_Source_Divide_By_2
1, 2
FOUT_TIMEBASE
FOUT_Timebase_Select
1, 2
SERIAL_TIMEBASE
DIO_Serial_Out_Divide_By_2,
Slow_Internal_Timebase
1, 2
Table 10-1.
Timebases Derived from IN_TIMEBASE (Continued)
Timebase
Related Bitfields
Divide Options
