SIM10M digital input is not normal digital inputs where you apply a certain voltage. These digital inputs does only detect a closed circuit (to ground, "sinking currentt")
When an input is connected to ground, a small current is generated (1mA limited by internal 2.2kOhm resistor) and measured by the SIM, and a pulse is recorded. The pull-up resistor is 2.47 kohm.
The minimum pulse length is 5 ms, with maximum frequency 8Hz.
The maximal cable length between meter and SIM digital input can be up to 80 meters but it's recommend 40 meters.
When an input is connected to ground, a small current is generated (1mA limited by internal 2.2kOhm resistor) and measured by the SIM, and a pulse is recorded. The pull-up resistor is 2.47 kohm.
The minimum pulse length is 5 ms, with maximum frequency 8Hz.
The maximal cable length between meter and SIM digital input can be up to 80 meters but it's recommend 40 meters.