ADLINK USB-1903 - Manual (Page 53)

Operation 39
USB-1900 Series
Continuous Scanning with Internal Hardware Timer
This mode is recommended if a fixed and precise A/D sampling
rate is required. You can accurately program the period
between conversions of individual channels. At least four coun-
ters must be specified, as follows.
X SI_counter (32-bit)
Specify the Scan Interval = SI_counter / timebase
X
SI2_counter (32-bit)
Specify the Data Sampling Interval = SI2_counter/timebase
X
PSC_counter (32-bit)
Specify the Post Scan Calculates after a trigger event
X
NumChan_counter (32-bit)
Specify the number of samples per scan
Acquisition timing and meaning of the four counters are as fol-
lows.
Figure 4-3: Analog Input Scan Timing