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SCADALink SS20 SCADASwitch User Guide

This guide has topics that are specific to the SCADALink SS20 SCADASwitch. Click the logo to return to this home page.

In addition to this guide you can use SCADALink SS20 SCADASwitch Product Page to obtain further information.

Telephone and email support are available at:

Click this to get the SS20 GUI installers. View the README.txt and CHANGELOG.txt for details.

Download the latest version


The SCADALink SS20 SCADASwitch is a communications multiplexer designed for SCADA and automation applications requiring communications to a single serial port on an RTU device to be polled from two independent hosts.

The SS20 enables serially connected devices such as PLC's, RTU's, Flow Computers, Data Loggers and Radio Modem Networks to be shared by SCADA Hosts, DCS, Master PLC's, HMI's, Maintenance software, and Local Operator Interfaces without contention on the serial bus.



The SS20 can simultaneously perform all of the following functions.

Multiplexing Allows two host or master devices to communicate asynchronously over a single serial channel. The SS20 buffers the serial traffic from both sources, and arbitrates the transactions to avoid collisions and lost data. (Note: only poll/response protocols such as Modbus or ROC are compatible *New support for Bristol BSAP protocol!)
(See Multiplexing for more information)
Modbus Address Translation/Blocking The SS20 can translate the address of an incoming Modbus poll to any other valid Modbus address and then translate the response back to the original address. This allows two different networks to connect to the same slave device on two different addresses.
(See Address Blocking / Translation for more information)
Modbus Broadcast Allows slave devices to simultaneously receive broadcast messages on any specified addresses. This allows for easy time-synchronization and shut-down commands even in mixed RTU networks
(See Address Blocking / Translation for more information)
Modbus Write Blocking By blocking Modbus write commands to an RTU from a specific input port, this feature can be used to grant read-only access to one SCADA host while allowing full access to a second host.
(See Write Protection for more information)
Communications Watchdog The SS20 can be configured to monitor traffic through its input ports and indicate if communications have failed via an integrated relay output.
(See Com Watchdog for more information)
LOI Local operator interface. Allows dedicated access to downstream devices (RS-232/RS-485) from a local computer via integrated USB connection without the need to physically disconnect the SCADA host or change any wiring.
(See LOI for more information)
Data Tap The SS20 can stream the hex data from all transactions through the USB interface to the integrated Data Tap window in the GUI or any other generic ASCII terminal for easy diagnostics and troubleshooting of communication problems.
(See Data Tap for more information)
RS-232 Radio Modem Keying Allows an RTU with no handshaking signals to key a radio or modem that requires RTS.
RS-485 Conversion Dual format output port allows host RS-232 connections to connect directly to both RS-232 and RS-485 slave devices.


For a detailed description of the hardware features see:

For current ratings, certifications, and other hardware specifications see:


The SCADALink SS20 is configured using a GUI1) connected via the USB port. This guide describes how to install and use this configuration tool.

When you start the GUI it will display this window.


The GUI screen layout has four main parts:


Before you can connect to the SS20's USB port, you must first install the USB drivers, then install the SS20 GUI software.


Use tool tips and built-in help to get more information.

The menu is the bar at the top of the main window that has these choices:

The navigation pane is the tree structure on the left side of the main window. It is used to navigate between forms. Each form has a set of related configuration parameters.


The forms are organized into these categories:

Status Bar

There is a bar at the bottom of the main window that has three text fields.

Status Message The left text box is a status area that has warnings, errors, and informative messages. It is cleared by clicking it, by clicking an entry in the navigation pane, or by clicking File > New.
Connection Status The middle text box indicates whether the GUI is connected to the SS20 or not. This box has the two values 'Connected' or 'Not Connected'.
Connection Port Identifier The right text box shows the serial port used to connect to the device.


This shows one possible usage of the SS20.

graphical user interface
start.txt · Last modified: 2023/10/04 06:04 (external edit)