Chapter 5 — About the GPIO Ports
Open Collector Input Interface Example
The input can be connected to an open collector interface of an external
device. This open collector input interface typically implies that the
grounds are tied together for the two systems. The common ground can
be a source of input noise, so you should follow good grounding
practices for both the reader and the input device.
In this situation, the reader provides power to the pull-up resistor for the
open collector. Connect the +Input pin to the +5 VDC source.
Open Collector Input Interface
IF1 Fixed RFID Reader User Manual