ADLINK PXI-2022 - Manual (Page 39)

Function Block and Operation Theory 31
4.4 Trigger Sources
In addition to the internal software trigger, the PXI-2020/2022 sup-
ports external digital triggers from the front panel connector
AFI[0…7], SMB TRIG I/O, PXI_STAR triggers, PXI Trigger Bus
Line 5. You can configure the trigger source by software com-
mand. Please refer to Figure 4-6 for trigger architecture.
Figure 4-6: PXI-2020/2022 Trigger Sources
4.4.1 Software Trigger
Software trigger is generated by software command. The trigger
asserts right after executing specified function calls to begin the
operation. This is the easiest way to acquire a single A/D data.
The A/D converter starts one con-version whenever the dedicated
software command is executed. Then the software would poll the
conversion status and read the A/D data back when it is available.
This method is very suitable for applications that need to process
A/D data in real time. Under this mode, the timing of the A/D con-
version is fully controlled under software. However, it is difficult to
control the A/D conversion rate.
4.4.2 External Digital Trigger
An external digital trigger occurs when a TTL rising edge or a fall-
ing edge is detected at the SMB connector TRG IO on the front
panel. As illustrated in Figure 4-7, the trigger polarity can be
selected by software. Note that the signal level of the external dig-
ital trigger signal should be TTL-compatible, and the minimum
pulse width is 12.5 ns.
Tr
igger S
ou
rce Mux AFI[0:7]
PXI
In
te
rf
ac
e PXI_STAR
PXI Trigger Bus Line 5
Software Trigger
TRG I/O
SMB Connector Digital Trigger Input
Trigger
Decision
T
rigger Output Mux
TRG I/O
SMB Connector
PXI Trigger Bus[5]
PX
I Inter
fa
ce
SSI_AD_TRIG
SSI_START
To Internal
Circuit
Digital Trigger Input
SCS
I