Digital Logic Inputs - Polycom SoundStructure C16 Design Manual

The pin out of the rear-panel DB25 connectors is shown in the figure.
Rear Panel DB25 Connector Pin Out
Logic inputs have a value that is read as either 0 or 1, logic outputs have a value that is set to either 0 or 1,
and the analog gain inputs have a value that varies from 0 to 255. The details of how to use logic pins are
described in the following sections.

Digital Logic Inputs

1
Logic inputs allow one to connect push to talk buttons and other dry contact closures to the rear-panel of
a SoundStructure device. The circuitry behind each logic input, shown in the following figure, shows that the
logic inputs have a default value of 1 due to the internal pull-up resistor.
1. A dry contact closure is one where there is no voltage externally applied to the contacts – it is simply an
open or closed circuit.
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