Chapter 4 Programming
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National Instruments Corporation 4-53 PCI E Series RLPM
Refer to the Analog Trigger section of Chapter 10, Miscellaneous
Functions, in the DAQ-STC Technical Reference Manual for information
about the analog trigger functionality of the DAQ-STC. The various modes,
Low Window, High Window, Middle Window, and high and low hysteresis
are discussed. The High Value and Low Value signals are controlled by two
DACs. For the PCI-6052E, PCI-MIO-16E-1, PCI-MIO-16E-4, and
PCI-6071E, these correspond to DACs 11
1
and 12 in the MB88341, which
contain 8-bit DACs. For the PCI-MIO-16XE-10, PCI-6031E, PCI-6032E,
and PCI-6033E, these correspond to DACs 0 and 1 in the AD8522, which
contains 12-bit DACs. For more information about the MB88341, and
AD8522, see Chapter 5, Calibration, in this manual.
One of two sources may be used as the trigger source, the PFI0/TRIG1
input on the I/O connector or an analog input passing through the PGIA.
The PGIA allows you to apply gain to an external signal for more flexible
triggering conditions. The PFI0/TRIG1 pin has an input voltage range of
±10 V. The Int/Ext Trig bit in the Misc Command Register controls which
input is used. The PGIA output is selected when this bit is set, and the
PFI0/TRIG1 input is selected when this bit is cleared. When the
PFI0/TRIG1 input is being used for an analog signal, it must be
disconnected from the DAQ-STC PFI input. You can do this by clearing
the Analog_Trigger_Drive bit in the DAQ-STC. When the
Analog_Trigger_Drive bit is set, the PFI0/TRIG1 pin is connected to PFI0
on the DAQ-STC.
The high and low thresholds are set by the DACs to be within plus/minus
full scale. For the 8-bit DACs, writing 0x00 sets it for + full scale, while
writing 0xFF sets it to – full scale. For the 12-bit DACs, writing 0x000 sets
it for + full scale, while writing 0xFFF sets it to – full scale. The selected
input is compared against each of these thresholds by a comparator. The
outputs of each comparator go high when the input voltage is greater than
the threshold. The outputs of these two comparators are connected to the
DAQ-STC analog trigger inputs 0 and 1. The DAQ-STC circuitry uses
these digital signals to generate the different slope and level detection
modes. See the DAQ-STC Technical Reference Manual for their
appropriate use. Figure 4-1 shows the analog trigger structure.
1
When writing to CALDAC 11, also write the same value to CALDAC 0.
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