Chapter4 HardwareOverview
©NationalInstruments Corporation 4-13 NI5102 User Manual
Table4-7 describes the pretrigger acquisition signals.
Table4-7. PretriggerAcquisition Signals
Signal Description
Start Trigger Starts data acquisition. In pretrigger mode, the Start Trigger signal
enablest he storage of pretrigger data. Start Triggercan only be
generated through software in pretrigger mode.
Scan Clock Causesthe ADC to convert the input signal into digital data. This signal
is also used in the memory controller to write the data into onboard
memory.This signal can be generated internally, with a 24-bit down
counterclocked with a 20 MHz signal to generate pulses from 20 MHz
to 1.19 Hz. The 24-bit counter providesa wid ec hoice of valid
frequenciesfor the Scan Clock signal. In additio n, Scan Clock can also
beselected from CH0, CH1, TRIG, PFI1, and PFI2, or any of the seven
RTSIbus trigger lines. RTSI bus trigger lines are available only on the
NI 5102 (PCI, PXI, ISA).
Scan Counter
TerminalCount
Is an internally generated signal that pulses once to indicate that the
pretriggersample count requirement is met. Betweenthe time when
thissignal pulses and the Stop Trigger occurs, hardware overwrites the
oldestpoints inmemory with the most recent points in a circular
fashion.All Stop Triggers occurring before Scan Counter Terminal
Count are ignored byth e device.
Stop Trigger Terminatesthe acquisition sequence after acquiring the posttrigger
samplecount. This trigger can b e generated through software, or CH0,
CH1,TRIG, PFI1, and PFI2, or any of the seven RTSI bus trigger lines.
RTSIbus trigger lines are available only on the NI 5102 (PCI,
PXI,ISA).
End of Acquisition Indicates end of acquisition to the control logic in the hardware.
It is generated from a counter that keeps track of points remaining
toacq uire. Itcan b eexported from the device on the PFI lines.