USB to Serial Converters Manual
Version 2.1
Document Reference No.: CP_000032 Clearance No.: CP#022
Copyright © Connective Peripherals Pte Ltd
13
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. Fitting more than one set of bias resistors can cause
overloading of the line drivers leading to unreliable operation of the unit and the overall system. Biasing
is not required for RS232 and may affect the signals if enabled.
ES-U-xxxx-x converters have four jumpers to select biasing on Tx+, Tx-, Rx+ and Rx-. The product-
specific sections throughout chapter 4 describe these in more detail.
When using RS-485 half-duplex, the
Tx and Rx pairs are combined into a single bi-directional pair and so only the jumpers for Tx biasing (
Pull
up of Tx+
and
Pull down of Tx-
) should be fitted. The Rx biasing should be disabled.
4.2
ES-U-2x01B / ES-U-2x01C Adapters (Plastic Enclosure)
This section applies to the following adapters:
•
ES-U-2001B
(see note below)
•
ES-U-2001C
(see note below)
•
ES-U-2101B
(see note below)
•
ES-U-2101C
(see note below)
Note:
This section applies
only
to revision B and C units which have the part numbers listed above. For
the original ES-U-2001 and ES-U-2101, please refer to version 1.4 of this guide which is available from
the Connective Peripherals website.
This section does not apply to ES-U-2xxx-M (metal case) adapters. Please see sections 4.3 and 4.4 for
these products.
See the General Notes and Warnings on page 12 before changing settings or opening the cover.
The jumpers should be set to select the correct serial mode before connecting the converter to
your RS-422/RS-485 serial bus.
DIP Switch Settings
On the inside of the unit, there are three DIP switches, which are used to select the required serial mode
(RS-422 or RS-485).
Operation Mode
S1
S2
S3
RS-422
4 Wire with handshaking
ON
ON
ON
RS-485
Full Duplex (4 wire)
OFF
ON
ON
Half Duplex (2 wire) with Echo
OFF
OFF
ON
Half Duplex (2 wire) without Echo
OFF
OFF
OFF
Table 2 - RS-422 & RS-485 Mode Configuration
Jumper Settings
Inside the unit, there is a 7x3 (21 pin) header block. Jumpers are used to select features such as 120
Ohm termination on Tx, Rx and CTS, and 750 Ohm biasing resistors on Tx and Rx. You will need to open
the cover and set the jumpers as per the requirements of your application.
Jumper
Function
1 - 2
Enable Tx+/- Termination with 120 Ohm (see notes below table)
2
–
3
Disable Tx+/- Termination
4
–
5
Enable Tx Bias - Pull-up Tx+ to VCC by 750 Ohm Bias resistor (see notes below table)
5
–
6
Disable Pull-up of Tx+ to VCC
7
–
8
Enable Pull-down of Tx- to GND by 750 Ohm Bias resistor (see notes below table)
8
–
9
Disable Pull-down of Tx- to GND
