28 
OSDP reader check: once the connection with the 
reader is properly established and configured, the Multi 
and the reader are switched on; the bi-color LED (Red 
and Green) must blink regularly. Red color indicates 
transmission where green color receiving. 
 
 
Figure 12 - OSDP readers, communication LED positions 
RS485 line length setting 
On Multi device there is a series of switches used, when OSDP 
readers are connected, to select RS-485 matched distance mode. 
Multi supports biasing and end-of-line termination for the RS-485 
network. Please refer chapter “Switches and LEDs” on page 61 for the 
position of the switches. 
 
For every reader there are two switches, one for Data A and one for 
Data B that need to be set both in the same way: 
 
•  When switch is OFF (terminator resistor is not inserted) RS-485 
allows the wiring of single-drop communication network of up to 
15 m in length. 
•  When switch is ON (terminator resistor is inserted) RS-485 
allows the wiring of single-drop communication network of up to 
1200 m in length.