User manual

Chapter Two Installation
man_905-105_2.9 Page 23
used to interconnect modules to reduce potential Radio Frequency Interference (RFI). An RS485
network should be wired as indicated in the diagram below and terminated at each end of the
network with a 120 ohm resistor.
The 905U modules include a terminating resistor on-board. If the 905U module is the first or last
module in the RS485 chain, then the terminating resistor may be connected by operating the single DIP
switch in the end-plate next to the RS485 terminals. “On” or “down” means that the resistor is
connected. The 105S does not have the terminating resistor built onto the board and must be added
externally.
A B
TERMINATING
RESISTOR SWITCH
905U
105S
RS485
A B
905U
105S
RS485
A B
905U
105S
RS485
A B
905U
105S
RS485
A B
Activate resistor-connection
switch at both end modules