Chapter 4 Hardware Overview
© National Instruments Corporation 4-13 NI 5102 User Manual
Table 4-7 describes the pretrigger acquisition signals.
Table 4-7. Pretrigger Acquisition Signals
Signal Description
Start Trigger Starts data acquisition. In pretrigger mode, the Start Trigger signal
enables the storage of pretrigger data. Start Trigger can only be
generated through software in pretrigger mode.
Scan Clock Causes the ADCto 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
counter clocked with a 20 MHz signal to generate pulses from 20 MHz
to 1.19 Hz. The 24-bit counter provides a wide choice of valid
frequencies for the Scan Clock signal. In addition, Scan Clock can also
be selected from CH0, CH1, TRIG, PFI1, and PFI2, or any of the seven
RTSI bus trigger lines. RTSI bus trigger lines are available only on the
NI 5102 (PCI, PXI, ISA).
Scan Counter
Terminal Count
Is an internally generated signal that pulses once to indicate that the
pretrigger sample count requirement is met. Between the time when
this signal pulses and the Stop Trigger occurs, hardware overwrites the
oldest points in memory with the most recent points in a circular
fashion. All Stop Triggers occurring before Scan Counter Terminal
Count are ignored by the device.
Stop Trigger Terminates the acquisition sequence after acquiring the posttrigger
sample count. This trigger can be generated through software, or CH0,
CH1, TRIG, PFI1, and PFI2, or any of the seven RTSI bus trigger lines.
RTSI bus 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
to acquire. It can be exported from the device on the PFI lines.
