ADLINK USB-1210 - Manual (Page 34)

24 Operation & Calibration
Software Conversion with Polling Data Transfer Acquisi-
tion Mode (Software Polling)
Generally the most convenient way to acquire a single A/D data
sample, the A/D converter starts a conversion when the dedicated
software command is executed. The software then polls the
conversion status and reads back the A/D data when it is
available.
This method is indicated when there is a need to process A/D data
in real time or instant closed-loop control. In this mode, the timing
of the A/D conversion is fully controlled by the software.
Continuous Acquisition Mode
Continuous A/D Conversion Clock Source
When the onboard ADC receives a conversion clock signal,
A/D conversion is triggered. The USB-1210 conversion clock
may originate with the internal hardware timer or externally via
CONV (external A/D conversion clock) pin. While the conver-
sion clock source can be chosen by setting AI source configu-
ration, if precision acquisition is required, use of the internal
hardware timer is recommended.
Sampling Rate Control with Internal Hardware Timer
This mode is recommended if a fixed and precise A/D sampling
rate is required.The period between conversions of individual
channels can be accurately programmed. ADC sampling rate is
determined by:
Sampling Rate = 2M/ScanIntrv Where ScanIntrv is scan
interval counter, value can be 1, 2, 3, 4… 2
32
- 1
WARNING:
The A/D conversion rate is determined by the software timer
and may not be precise.