Digital Input Debounce Filter - Advantech PCI-1716 User Manual

3.3.5

Digital Input Debounce Filter

To prevent false results such as redundant interrupts (as shown in Figure 3.23) due
to noise or bouncing in the digital input signal, the digital input debounce filter can be
enabled. When enabled, transient pulses with duration shorter than the filter duration
will be considered as glitches and will not present in the filtered digital input signal.
The transition of the original signal propagates to the filtered signal only after it is sta-
ble for at least filter duration. This is shown in Figure 3.24.
Figure 3.23 Digital input without debounce filter.
Figure 3.24 Digital input with debounce filter.
When the digital input debounce filter is enabled, an internal filter sample clock is
enabled accordingly. The half-period of the filter sample clock is equal to the config-
ured filter duration. The digital input signal is sampled at each rising edge and falling
edge of the filter sample clock. The transition of the original signal propagates to the
filtered signal only when it is stable for two consecutive filter sample clock edges as
shown in Figure 3.25. Due to the uncertainty of relative time between original signal
edge and filter sample clock edge, transient pulse of the original signal with width
between 1 to 2 times the filter duration may or may not be filtered. However, pulse
width which is longer than 2 times the filter duration will not be filtered, and that is
shorter than the filter duration will be filtered.
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