National Instruments DAQ M Series - Manual (Page 99)

Chapter 7 Counters
© National Instruments Corporation 7-37 NI 6236 User Manual
Enabling Duplicate Count Prevention in NI-DAQmx
You can enable duplicate count prevention in NI-DAQmx by setting the
Enable Duplicate Count Prevention attribute/property. For specific
information about finding the Enable Duplicate Count Prevention
attribute/property, refer to the help file for the API you are using.
Synchronization Modes
The 32-bit counter counts up or down synchronously with the Source
signal. The Gate signal and other counter inputs are asynchronous to the
Source signal, so M Series devices synchronize these signals before
presenting them to the internal counter.
M Series devices use one of three synchronization methods:
• 80 MHz source mode
• Other internal source mode
• External source mode
In DAQmx, the device uses 80 MHz source mode if the user performs the
following:
• Performs a position measurement
• Selects duplicate count prevention
Otherwise, the mode depends on the signal that drives Counter n Source.
Table 7-6 describes the conditions for each mode.
Table 7-6. Synchronization Mode Conditions
Duplicate Count
Prevention Enabled
Type of
Measurement
Signal Driving
Counter n Source
Synchronization
Mode
Yes Any Any 80 MHz Source
No Position Measurement Any 80 MHz Source
No Any 80 MHz Timebase 80 MHz Source
No All Except Position
Measurement 20 MHz Timebase,
100 kHz Timebase,
or PXI_CLK10 Other Internal Source
No All Except Position
Measurement Any Other Signal
(such as PFI or RTSI) External Source