Bausch Datacom DinBox RTU M4 Reference Manual page 31

RTU I/O
Configuration of the local digital input's.
The DinBox RTU M4 has 8 digital inputs. All inputs are active; the input line must be
short-circuited with the common input to activate an input.
Rising or positive slope: when the input line is connected to the common input.
Falling or negative slope: when the input line is disconnected from the common input.