ADLINK DAQe-2214 - Manual (Page 86)

74 Operation Theory
EXTDTRIG and EXTWFTRIG
EXTDTRIG and EXTWFTRIG are dedicated digital trigger input
signals for A/D and D/A operations. Refer to section 4.5 for
details.
EXTTIMEBASE
When the applications needs specific sampling frequency or
update rate that the card could not generate from its internal
TIMEBASE — the 40 MHz clock — you could utilize the EXT-
TIMEBASE with internal counters to achieve the specific timing
intervals for both A/D and D/A operations. Note that once you
choose the TIMEBASE source, both A/D and D/A operations
will be affected because A/D and D/A operations share the
same TIMEBASE.
AFI[0]
Alternatively, you can also directly apply an external A/D con-
version signal to replace the internal ADCONV signal. This is
another way to achieve customized sampling frequencies. The
external ADCONV signal can only be inputted from the AFI[0].
As section 4.1 describes, the SI_counter triggers the genera-
tion of the A/D conversion signal, ADCONV, but when using
the AFI[0] to replace the internal ADCONV signal, the
SI_counter and the internally generated SCAN_START is not
effective. By controlling the ADCONV externally, you can sam-
ple the data according to external events. In this mode, the
Trigger signal and trigger mode settings are not available.
AFI[0] could also be used as SCAN_START signal for A/D
operations. Refer to section 4.1 and section 4.6 for detailed
descriptions of the SCAN_START signal. When using external
signal (AFI[0]) to replace the internal SCAN_START signal, the
pulse width of the AFI[0] must be greater than two time of the
period of Timebase. This feature is suitable for the DAQ-2200/
DAQe-2200/PXI-2200 Series, which can scan multiple chan-
nels data controlled by an external event. Note that the AFI[0]
is a multi-purpose input, and it can only be utilized for one func-
tion at any one time.