USB to Serial Converters Manual
Version 2.0
Document Reference No.: CP_000032 Clearance No.: CP#022
Copyright © Connective Peripherals Pte Ltd
23
5
Switch and Jumper Settings
This section applies to ES-U-2xxx-x and ES-U-3xxx-x converters, which can be configured for different
interface types. These converters have DIP switches and internal jumpers to select the required interface.
The following pages give details of the settings required for each particular model of converter. Ensure that
you refer to the correct section for your model of converter. The relevant model numbers are listed at the
top of each section. Always read the general notes and warnings on this page before proceeding to
configure your device.
5.1
General
Notes and
Warnings
Safety
For ES-U-xxxx-RM models with internal power supplies, the power cable must be disconnected
before removing the cover. Opening the cover will expose connections and boards carrying lethal
voltages. Contact with these will cause severe injury or death. In common with all switching power
supplies connected to the mains (120/240VAC), the power supply board in these products can
remain charged with dangerous voltages for some time after the power input is disconnected and
so avoid contact with the power supply board inside the converter even when un-powered.
Serial Bus Configuration
It is important to configure the DIP switches and jumpers to select the correct type of serial bus (RS-232,
RS-422 or RS-485) for your application before connecting the ES-U-xxxx-x converter to your serial bus.
Otherwise damage can occur to the converter or other equipment on the RS-232/RS-422/RS-485 bus.
To avoid damage, the power supply (or power cable in rack-mount units), serial cables and USB cable
should be disconnected from your converter before changing DIP switch settings and before opening the
case to change jumper settings.
Termination
For RS-422 or RS-485, it may be necessary to enable termination of the data transmission lines. This
depends on the way in which your network is connected and if termination is already provided by other
devices on the network. Before applying the termination, check your cable specification for proper
impedance matching. Termination is not needed for RS232 and may affect the signals if enabled.
Termination is normally used in the node at each end of the bus, but nodes in the middle of the bus should
not have termination enabled. The ES-U-xxxx-x converters have jumpers (or DIP switches) to allow internal
termination resistors to be enabled if required. This avoids the need to provide an external resistor at the
ES-U-xxxx-x end of the bus.
ES-U-xxxx-x converters have jumpers/switches for both Tx +/- termination and Rx +/- termination. When
using RS-485 half-duplex, only the Rx +/- termination should be enabled as indicated by the comments in
the jumper / switch setting tables for each product.
Biasing
For RS-485 half-duplex, it may be necessary to enable biasing of the data transmission lines. In some
cases, the RS-485 lines may float to undefined levels when no transmitter is active, and this can cause
additional unexpected characters to appear at the start or end of a message. Biasing resistors are used to
set a defined logic level on the serial lines when no node is transmitting.
Some ES-U-xxxx-x models feature internal 750 ohm resistors with jumpers to enable/disable them. These
should be disabled if another device on your serial bus already provides biasing as biasing of data lines
must only occur at a single point in the cabling. They are not required in RS-422 or RS-485 full-duplex,
since the transmitter is always enabled. Biasing is not required for RS232 and may affect the signals if
enabled.
