Understand the differences between how a Wiegand setup and an OSDP over RS-485 setup works.
Wiegand
Wiegand interfaces use a multi-pin configuration to connect to the reader. Each pin has a dedicated function, and the data transmission is uni-directional, using one pin to signal the zeros (0) and another for the ones (1). The other pins are dedicated to the power, beep, and green and red LEDs.
OSDP over RS-485
In an OSDP over RS-485 setup, the data transmission is bi-directional, and uses a differential twisted pair with 120 ohms of characteristic impedance to exchange data between the reader and the interface. All functions, such as LED, beep, and so on, are achieved through this single connection.