USB to Serial Converters Manual
Version 2.1
Document Reference No.: CP_000032 Clearance No.: CP#022
Copyright © Connective Peripherals Pte Ltd
16
Switch S4 selects 120R termination of TxD. It is normally enabled for half-duplex RS-485 modes but may
not be required if both ends of your network are already terminated.
Jumper Settings
Inside the unit, there is a 6x2 (12 pin) header block for each serial port. Jumpers are used to select
features such as 120 Ohm termination on 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 Bias - Pull-up Tx+ to VCC by 750 Ohm Bias resistor (see notes below table)
3 - 4
Enable Tx Bias - Pull-down Tx- to GND by 750 Ohm Bias resistor (see notes below table)
5 - 6
Enable Rx+/- Termination with 120 Ohm (see notes below table)
7 - 8
Enable Rx Bias - Pull-up Rx+ to VCC by 750 Ohm Bias resistor (see notes below table)
9 - 10
Enable Rx Bias - Pull-down Rx- to GND by 750 Ohm Bias resistor (see notes below table)
11 - 12
Enable CTS Termination with 120 Ohm (populate for RS422 mode if termination is
required)
Table 7 - Jumpers to select Termination and Biasing
Note on Termination:
For RS485 half-duplex, if termination is required, only Tx Termination should be enabled as the Tx and
Rx lines are linked. Enable Tx+/- termination (using DIP switch 4 on this model) and disable Rx+/-
termination (leave jumper 5-6 open)
For RS485 full-duplex and RS422, termination can be enabled/disabled for Tx+/- and Rx+/- pairs
independently using the jumpers as required. See the notes on Termination in section 4.1 before setting
these options
Note on Biasing:
For RS485 half-duplex, if biasing is required, enable Tx+/- biasing only (jumper 1-2 and 3-4) and disable
Rx+/- biasing (leave jumper 7-8 and 9-10 open).
For RS485 full-duplex and RS422, biasing can be enabled/disabled for Tx+/- and Rx+/- pairs
independently as required. See the notes on Biasing in section 4.1 before setting these options
4.5
ES-U-3xxx-x and ES-U-2101-MB
This section applies to the following adapters:
•
ES-U-3001-MB
•
ES-U-3008-RM
•
ES-U-3016-RM
•
ES-U-2101-MB
See the General Notes and Warnings on page 12 before changing settings or opening the cover.
The DIP switches should be set to select the correct serial mode before connecting the converter
to your RS-232/RS-422/RS-485 serial bus.
DIP Switch Settings
On the outside of the unit, there are four DIP switches, which are used to select the required serial mode
(RS-232, RS-422 or RS-485).
Operation Mode
S1
S2
S3
S4
RS-232
OFF
ON
ON
ON
