MPA2C3 Installation Guide 55
OSDP Bus termination
Because OSDP is an RS485 protocol, for long distances the balanced RS485A and
RS485B signal wires must be terminated at both ends of the OSDP reader cable
with an 120 Ohm resistor.
Because there are 2 OSDP RS485 busses (OSDP1 and OSDP2), for each OSDP bus
this has to be set up correctly.
The below tables give examples of readers connected to various RJ45 terminals
and the DIP Switch SW2 setting and resistor placement at the reader.