ADLINK DAQe-2502 - Manual (Page 33)

Operation Theory 23
Acquisition Modes
Software Polling
This is the easiest way to acquire a single A/D data. The A/D
converter starts one conversion whenever the dedicated soft-
ware command is executed. Then the software would poll the
conversion status and read the A/D data back when it is avail-
able.
This method is very suitable for applications that needs to pro-
cess A/D data in real time. Under this mode, the timing of the
A/D conversion is fully controlled by the software. However, it is
difficult to control the A/D conversion rate.
Programmable Scan
This method is suitable for applications that need to acquire A/
D data at a precise and fixed rate. A scan is a group of multiple
channel samples and the scan interval is defined by the
SI_counter. Likewise, the sample interval of the multiple chan-
nels is defined by the SI2_counter. Refer to Table 4-4 for more
information.
The DAQ-/DAQe-/PXI-2502/2501 card can sample multiple
channels in continuous/discontinuous ascending sequence.
For example, you may program the DAQ-/DAQe-/PXI-2502/
2501 card to perform a scan in the channel sequence of 1-2-4-
1-2-4. Three trigger modes are available in programmable
scan: post-trigger, delay-trigger, and post/delay-trigger with
retrigger. Refer to Table 4-3 for a brief summary on trigger
modes and their trigger sources.
Trigger Mode Description Trigger Sources
Post-Trigger
Perform a scan right after the trigger
occurs.
Software Trigger
Digital Trigger
Analog Trigger
SSI AD Trigger
Delay-Trigger
Scan delayed by the amount of time
programmed after the trigger.
Post/Delay-Trigger
with Retrigger
Perform repeated scan while trigger
occurs and it could be under Post-
Trigger or De-lay-Trigger mode.
Table 4-3: Trigger Modes and Corresponding Trigger Sources