Revised 2016-02-12
Hardware Installation
Serial RS485 Wiring
2-26
Sixnet
®
SeriesRAM
®
9000
Hardware Guide
Bias Resistors:
On a RS485 2-wire network, a pair of bias resistors (1K ohm typically) acting upon the transmit/
receive wires may be required. If bias resistors are not present, the receive inputs on some RS485 devices may
react to noise on the floating wires. The bias resistors will force the transmit/receive wires to a known (non-floating)
state when none of the RS485 devices are transmitting data. Some RS485 devices have bias resistors built-in and
are enabled through DIP-switch or jumper settings. Make sure there is only one pair of bias resistors acting upon
the network. The RAM 9000 provides a way to easily connect external biasing resistors if needed. To bias the
RS485+ connect a resistor of the desired value between the VBIAS terminal and the RS485+ terminal. To bias the
RS485- connect a resistor of the desired value between the IGND terminal and the RS485- terminal. As mentioned
above, 1K ohms is a typical value for a biasing resistor but other RS485 devices may recommend other values.
Note:
The RAM 9000 RS485 port is designed in such a way as to never need biasing, but it
includes the VBIAS screw as a convenience for use with 3rd party devices that require network
biasing but lack the VBIAS connection. If the RS485 network is made up exclusively of RAM 9000
devices, then these bias resistors are not necessary.
Note:
Terminals are sized to hold 28 to 12 gauge wire, 12 AWG wire area is 3.31mm2
Torque spec for terminals is 0.5 Nm.
Use copper wire rated to 90°C or above. (For IECEx/ATEX use copper wire rated to at least 107°C)
pin
name
description
RS485 (Top of unit)
IGND
Isolated
Ground
RS485 signal ground optically isolated from other
ground.
VBIAS
Voltage Bias
Connect to add RS485 Network Biasing.
TERM
Termination
Connect to add RS485 Network Termination.
485-
RS485-
Two wire RS485 negative terminal.
485+
RS485+
Two wire RS485 positive terminal.
