Polycom SoundStructure C16 Design Manual page 249

The logic inputs has a default value of 1 (high) when the contact closure is open, and has a value of 0 (low)
when the contact closure is closed and tied to ground.
Logic Input Circuitry
A typical contact closure example is shown in the following two figures. In the first figure, the input generates
the value 1 (high) because the switch is open.
Open Remote Control Contact Closure Example
When the logic switch is closed, as shown in the figure below, the logic value reads the value 0 (low)
indicating that the contact has been closed.
Closed Remote Control Contact Closure Example
The logic inputs are internally debounced and can detect changes in the contact closures as short as
100msec.
Polycom, Inc. 249