Rs485 Termination; Rs485 Biasing - HORNER APG EXL10 OCS User Manual

MAN1029-08-EN_EXL10_UserManual
Figure 10.1 – Serial Port Wiring & Dip Switches

10.4 RS485 Termination

Proper RS485 termination minimizes signal reflections and improves reliability.
Both the MJ2 and MJ3 serial ports allow an internal termination resistor to be placed across pins 1 and 2
by DIP Switch Setting.
Only the two devices physically located at the endpoints of the RS485 network should be terminated.

10.5 RS485 Biasing

RS485 biasing passively asserts a line-idle state when no device is actively transmitting, which is useful for
multi-drop RS485 networking.
Both the MJ2 and MJ3 serial ports allow internal bias resistors to be switched in, pulling Pin 1 up to 3.3V
and pulling Pin 2 down to ground. The Set Serial Ports item in the System Menu can be used to enable
RS485 biasing. Also, an application graphics screen that writes to %SR164 can do the same thing. Setting
%SR164.1 enables MJ2 biasing and setting %SR164.2 enables MJ3 biasing.
If biasing is used, it should be enabled in only one of the devices attached to the RS485 network.
t h
A p r i l 2 4 , 2 0 2 0 P a g e 107 | 191