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1.2.1 The RS485 Enable Signal
In a balanced differential system the data signals are produced by a line driver. The line driver generates a
voltage across a pair of signal wires that transmits the data signals. A balanced line driver can have an
optional input signal called an “Enable” signal. The purpose of the enable signal is to connect the driver to
its output terminals. If the enable signal is off, the driver is disconnected from the transmission line. When a
driver is disconnected from the network it is referred to as being in the “tri-state” condition. Because there
are multiple drivers (transmitters) on a RS485 network and only one transmitter can be enabled at a time, the
use of this enable control signal is required on all RS485 networks.
The XPort provides this enable signal for RS485 two-wire applications. When configured for RS485 two-
wire applications, the XPort automatically asserts the enable when it is ready to transmit data from its serial
port. Once the data has been transmitted, the XPort automatically de-asserts the enable signal to allow other
nodes to transmit their data.
1.2.2 NET485 Wiring
NOTE: You cannot configure the NET485 through the serial port. The boot program has no control over the
Configurable Pins, so the NET485 will never be able to send data during the boot period (initial 5 seconds).
The XPort can be configured to use any one of the three configurable PIO pins as the RS485_TXEN enable.
The NET485 uses CP1 for the transmit enable. You must enable CP1 for RS485_TXEN during the
configuration process. (See the Quick Start Guide for details)
Note: CP1 is the hardware designation for the XPort physical pin #6. In the web configuration menus, this pin is called
CP0.
You can set the active state of the control pins to LOW or HIGH. The NET485 uses CP1 in the Active High
condition. You must set CP1 to Active High during the configuration process. (See the Quick Start Guide
for details)
Note: CP1 is the hardware designation for the XPort physical pin #6. In the web configuration menus, this pin is called
CP0.
1-2 NET485 User Guide