Operation Theory
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EXTTIMEBASE
When the applications needs specific sampling frequency or update rate
that the card could not generate from its internal TIMEBASE, the 40MHz
clock, users could utilize the EXTTIMEBASE 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, users can also directly apply an external A/D conversion
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 generation of the A/D conversion signal, ADCONV,
but when using the AFI[0] to replace the internal ADCONV signal, then the
SI_counter and the internally generated SCAN_START will not be effective.
By controlling the ADCONV externally, users can sample the data ac-
cording to external events. In this mode, the Trigger signal and trigger
mode settings will are not available.
AFI[0] could also be used as SCAN_START signal for A/D operations.
Please refer to sections 4.1 and 4.6.1 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/PXI-2200 series, which can scan multiple channels data con-
trolled by an external event. Note that the AFI[0] is a multi-purpose input,
and it can only be utilized for one function at any one time.
AFI[1]
Regarding the D/A operations, users could directly input the external D/A
update signal to replace the internal DAWR signal. This is another way to
achieve customized D/A update rates. The external DAWR signal can only
be inputted from the AFI[1]. Note that the AFI[1] is a multi-purpose input,
and it can only be utilized for one function at any one time. AFI[1] currently
only has one function. ADLINK reserves it for future development.
4.6.3
System Synchronization Interface
SSI (System Synchronization Interface) provides the DAQ timing syn-
chronization between multiple cards. In DAQ/PXI-20XX series, we de-
signed a bi-directional SSI I/O to provide flexible connection between cards
and allow one SSI master to output the signal and up to three slaves to
receive the SSI signal. Note that the SSI signals are designed for card
synchronization only, not for external devices.
