Chapter4 HardwareOverview
©NationalInstruments Corporation 4-11 NI5102 User Manual
Pretrigger Acquisition
In pretrigger acquisition mode, the device acquires a certain number of
scans,called the pretrigger scan count, before the trigger occurs. After
satisfyingthe pretrigger scan count requirement, hardware keeps acquiring
dataand stores it in a circular buffer implemented in onboard m emory. The
sizeof the circular buffer equals the pretrigger scan count. When the trigger
occurs,hardware acquires and stores the posttriggerscans and the
acquisition terminates. Table 4-6 shows the minimum and maximum
number of samples available on the NI 5102 in pretriggered mode.
Note If Scan Clock is externallysupp lied, a free-running clock must be used for proper
operation.
Table4-6. Possible Number of Samples for Pretriggered Mode
Numberof Channels
NI 5102 (PCI, PXI) NI 5102 (ISA, PCMCIA, USB)
Min Max Min Max
One
Pretriggeredscans
Posttriggered scans
1
1
663,000
16,777,216*
1
1
663,000 –A
663,000 –B
Two
Pretriggeredscans
Posttriggered scans
1
1
331,500
16,777,216*
1
1
331,500 –A
331,500 –B
*Dependent on available memory
A–Thenumber of posttriggered scans
B–Thenumber of pretriggered scans