Document Reference No.: ES_000086

ES-R-2x01B-M RS-232 to RS-422/RS-485 Converters Manual

Version 1.0

Clearance No.: ES

©2010 - 2011 EasySYNC Ltd.

6

4 Hardware Installation

Serial Bus Configuration

It is important to configure the DIP switches and jumpers to select the correct type of serial bus (RS-422

or RS-485) for your application before connecting the ES-R-2x01B-M converter to your serial bus.

Otherwise damage can occur to the converter or other equipment on the bus.

To avoid damage, the power supply and serial cables 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 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-R-2x01B-M converters have jumpers to allow internal

termination resistors to be enabled if required. This avoids the need to provide an external resistor at the

ES-R-2x01B-M end of the bus.

Since a computer controlled serial port is normally at one end of the cable, termination is enabled by

default in the converter. If termination is not required, please disable this feature using the jumpers

inside the converter.

ES-R-2x01B-M converters have jumpers for both Tx ± termination and Rx ± termination. When using RS-

485 half-duplex, only the Tx ± termination should be enabled.

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. This can cause

additional unexpected characters to appear at the start or end of a message. Biasing resistors are used to

guarantee a defined logic level on the serial lines when no node is transmitting.

The ES-R-2x01B-M 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 typically not required in RS-422 and some

RS-485 full-duplex applications since the transmitter is always enabled.

The ES-R-2x01B-M converters have four jumpers to select biasing on Tx+, Tx-, Rx+ and Rx-. For biasing

of an RS-485 half-duplex bus, enable only the Rx biasing (Pull-up Rx+ to VCC by 750 Ohm Bias resistor

and Pull-down Rx- to GND by 750 Ohm Bias resistor). The Tx biasing (Pull-up Tx+ to VCC by 750 Ohm

Bias resistor and Pull-down Tx- to GND by 750 Ohm Bias resistor) should not be enabled as this would

provide two biasing resistors per line.