Filter Control
All the I/O input lines are fitted with a glitch-removal filter. The filter strength is user-configurable through the
LineFilterStrength
control.
The strength control provides 5 positions from 'Lowest' to 'Highest'. The default position is 'Low'.
Each position corresponds to a specific filter time constant for each of the 3 I/O input line types:
LineFilterStrength | Differential inputs (DIN) | TTL inputs (TTLIO) | Isolated Inputs (IIN) |
---|---|---|---|
Lowest | 50 ns | 50 ns | 500 ns |
Low | 100 ns | 100 ns | 1 µs |
Medium | 200 ns | 200 ns | 2 µs |
High | 500 ns | 500 ns | 5 µs |
Highest | 1 µs | 1 µs | 10 µs |
The user is invited to set the filter strength according to the quality of the external signal. Select a filter strength such that its time constant is:
- Greater than the longest glitch duration
- Greater than the 10%~90% rise/fall time of the signal
- At least 2 times smaller than the smallest signal pulse duration
The glitch removal filter introduces a latency into the input signal path. The latency is equal to the filter time constant when the incoming signal has clean transitions. The latency may increase significantly in case of bad quality signals.