Di Change Detection Applications; Digital Filtering - National Instruments X Series User Manual

Chapter 6 Digital I/O
The Change Detection Event signal can do the following:
• Drive any RTSI <0..7>, PFI <0..15>, or PXI_STAR signal
• Drive the DO Sample Clock or DI Sample Clock
• Generate an interrupt
The Change Detection Event signal can also be used to detect changes on digital output events.

DI Change Detection Applications

The DIO change detection circuitry can interrupt a user program when one of several DIO
signals changes state.
You can also use the output of the DIO change detection circuitry to trigger a DI or counter
acquisition on the logical OR of several digital signals. To trigger on a single digital signal, refer
to the Triggering with a Digital Source
Detection Event signal to a counter, you can also capture the relative time between bus changes.
You can also use the Change Detection Event signal to trigger DO or counter generations.

Digital Filtering

You can enable a programmable debouncing filter on each digital line on Port 0. When the filters
are enabled, your device samples the input on each rising edge of a filter clock. X Series devices
divide down the onboard 100 MHz or 100 kHz clocks to generate the filter clock. The following
is an example of low-to-high transitions of the input signal. High-to-low transitions work
similarly.
Assume that an input terminal has been low for a long time. The input terminal then changes
from low-to-high, but glitches several times. When the filter clock has sampled the signal high
on two consecutive edges and the signal remained stable in between, the low-to-high transition
is propagated to the rest of the circuit.
Filter Setting
Short
Medium
High
None
6-20 | ni.com
section of Chapter 11, Triggering. By routing the Change
Table 6-1. Filters
Filter Clock
12.5 MHz
195.3125 kHz
390.625 Hz
—
Pulse Width
Guaranteed to Pass
Filter
160 ns
10.24 µs
5.12 ms
—
Pulse Width
Guaranteed to Not
Pass Filter
80 ns
5.12 µs
2.56 ms
—