ADLINK PCI-9846 - Manual (Page 39)

Operation Theory 29
Table 3-1 shows several basic counters required for operating dig-
itizers.
Refer to Figure 3-4 and use post trigger mode as an example.
When a trigger is accepted by digitizer, the acquisition engine of
the digitizer will begin to acquire data that coming from ADC and
store these sampled data to onboard memory. The sampled data
is generated continuously at the rising edge of timebase according
to the scan interval counter setting. While sampled data reaches
customer specified number, in this example is 256, the acquisition
ends. Once the acquisition ends, acquisition engine begins to
send request to system and transfer data from onboard memory
back to system by DMA.
Counter Name Length Valid value Description
ScanIntrv 24-bit 1 - 16777215
Scan Interval Counter
This counter is a TIMEBASE divider to
the achieve equivalent sampling rate of
digitizer. The equation is:
Sampling rate = TIMEBASE / ScanIntrv
The value of TIMEBASE depends on the
card type. Take the PCI/PXI-9846
(40 MS/s) as an example, ScanIntrv = 1
results in 40 MS/s and ScanIntrv = 2
results in 20 MS/s, and so on.
DataCnt 29-bit 1 - 536870911
Data Counter
You can specify the amount of data to be
acquired. The digitizer equips 512MB
memory to store acquired data.
trigDelayTicks 32-bit 1 - 536870911
Delay Trigger Counter
The delay trigger counter is used to indi-
cate the time between a trigger event
and the start of an acquisition. The unit of
a delay count is the period of the TIME-
BASE. For PCI/PXI-9816, the unit is
100ns and for PCI/PXI-9846 the unit is
25ns. Refer to section 3.5.4 for more
detail.
ReTrgCnt 24-bit 1 - 16777215
Re-Trigger Counter
The digitizer can enable re-trigger to
accept multiple triggers. Refer to section
3.5.5 for more detail.
Table 3-1: Basic Counters