User's Manual

905U-E Wireless Ethernet Bridge User Manual

Man_905U-E Rev 1.0 Page 8

As the RS485 communication medium is shared, only one of the units on the RS485 cable may

send data at any one time. Thus communication protocols based on the RS-485 standard require

some type of arbitration.

RS485 is a balanced, differential standard but it is recommended that shielded, twisted pair cable

be used to interconnect modules to reduce potential RFI. It is important to maintain the polarity

of the two RS485 wires. 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. On-board 120 ohm resistors

are provided and may be engaged by operating the single DIP switch in the end plate next to the

RS485 terminals. The DIP switch should be in the “1” or “on” position to connect the resistor. If

the module is not at one end of the RS485 cable, the switch should be off.

HOST

905U-D

HOST

RS485 CONNECTIONS

120

Ω

RS485

SUPPLY

RS232

DIP SWITCH

FOR 120Ω

120

Ω

HOST HOST

905U-E

RS485 CONNECTION USING TERMINATING RESISTOR

ETHERNET

DIO

DEFAULTS DIP SWITCH

2.4 Digital Input/Output