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A: It detects automatically if AIN or DIN is used.
Hint:
Impulse counter can be configured by connecting DIN1 or DIN2 wire (one of them). If you will use DIN1 as impulse counter there is no any configuration needed, except enabling DIN1 I/O element.
Negative input can be configured by using only DIN2 wire, and this should be configured as "Ground sense" Input mode.