Document Reference No.: ES_000086
ES-R-2x01B-M RS-232 to RS-422/RS-485 Converters Manual
Version 1.0
Clearance No.: ES
#
42
©2010 - 2011 EasySYNC Ltd.
6
4
Hardware Installation
4.1
General Notes and Warnings
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.
