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HWg-ER84a: Serial, DI & DO (relays) over Ethernet

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Replaced by Other I/O & Serial products

I/O Controller HWg-ER84a is a Ethernet device server (RS-232/485) with I/O (8/4 relay contacts). Free Windows virtual serial port included. Industrial model, fits on

Serial port, inputs and outputs are controlled over a TCP/IP connection using a TELNET-like (RFC2217) M2M protocol. The protocol is fully documented (NVT), the Hercules SW terminal can be used for testing (supports inputs and outputs).

  • Relay outputs can be controlled from the command line with a simple HWg IPRC cmd utility.
  • The ER84a serial port can be connected to via a virtual serial port (e.g. COM27) on your networked PC. The HW VSP application for Windows is supplied free of charge.
  • Control the product from your own application in minutes.
    Make your work easier with many examples for various programming languages in the  HWg SDK (Borland C++ Builder, MS Visual C, VB, Delphi, C#, PHP, JAVA).


Box-2-Box mode: Two devices can be connected against each other to extend inputs, outputs, and the serial line over the Ethernet.

4 output relays, 8 inputs for contacts and a serial port over IP

Photo 1 Photo 2

a DIN rail. It is controlled over TCP/IP using a Telnet-like M2M protocol.


Basic features

  • RS-232/485 serial port
  • 8 binary inputs to connect contacts, buttons, or 7 to 24VDC
  • 4 built-in double-throw relays
  • Virtual serial port driver for Windows = easily get e.g. COM 5 on your PC

  • Industrial model, fits on a DIN rail
  • Ethernet interface for connecting to an IP network
    • Telnet-like M2M protocol
    • Support for TCP Server and TCP Client/Server modes
    • Box-2-Box mode


  • Four built-in relays can, for example, open a door, turn on a horn, or disconnect power – remotely over the network.
  • Connect your RS-232 devices to the network: barcode / RFID scanners, serial printers, displays.
  • Link up to eight buttons / switches with a SW application.


  • The Box-2-Box mode allows you to connect two units against each other.
    • Extension of RS-232 or RS-485 range over the network
    • Inputs at one device control outputs at the other device


M2M communication

I/O Controller ER84a, Telnet Relay, TCP relay outputs, RS-485 to IP, M2M serial ethernet, Device server with IO
  • TCP/IP Server   [Client -> Server]
    I/O Controller, as a TCP server, listens for incoming TCP connections from a computer (a PC or a server). When the connection is established, data in the internal buffer are transmitted, and then bidirectional communication can take place, similarly to a common "terminal server".
    Binary inputs and outputs can be controlled with a M2M protocol that uses an extension of RFC2217 (NVT support must be enabled).

  • TCP/IP Client/Server    [Server <- Client]
    I/O Controller has received some data into its internal buffer from the serial port (or has detected a change at the binary inputs) and attempts to send it to the server. The unit tries to establish a connection to the specified outgoing IP address and port. If unsuccessful, it waits for about one second in the TCP server mode and then tries to establish the connection again.
    Binary inputs and outputs can be controlled with a M2M protocol that uses an extension of RFC2217 (NVT support must be enabled and the TCP connection must be established).

  • UDP/IP
    Data are sent as UDP packets, without delivery acknowledgement.
    In the UDP mode, the device uses a sophisticated "packetiser" that allows you to specify broad conditions about what should be sent from the serial line to the Ethernet, what should not, and when.
    Binary inputs and outputs cannot be controlled in the UDP mode.

  • free virtual serial port  free virtual serial port, Device server with IO, RS-232 printer to EthernetVSP (Virtual serial port)
    The HW VSP software, when installed on a PC with Windows, creates a virtual serial port (e.g. COM7), and the serial port at the I/O Controller then works as a physical port of your PC.
    Binary inputs and outputs
    can be controlled from HW VSP using the "Binary I/O" tab, as long as NVT support is enabled for both the HW VSP software and the I/O Controller unit.



  • Software for Users
    • Hercules - configuration (IP address, Telnet setup) and testing utility for Windows
    • HWg IPRC cmd – command-line control of outputs
    • HW VSP - HW Virtual Serial Port for Windows.
      I/O Controller is also supported by the VSP Multi version that allows you to connect up to 64 serial ports to a single PC.
  • For programmers
    • Examples in the HWg SDK
      SDK (Software Development Kit) with examples of controlling the I/O Controller is available for download free of charge.

      • EX01: UDP Setup (Borland C++ Builder, MS Visual C, VB, Delphi, C#)
      • EX02: I/O Controller (Borland C++ Builder, MS Visual C, VB, Delphi, C#)
      • EX03: Control Remote Serial Port (Borland C++ Builder, MS Visual C, VB, Delphi, C#)
      • EX13: TCP Setup (Borland C++ Builder, MS Visual C, VB, Delphi, C#)
  • NVT (Network Virtual Terminal) M2M communication protocol


Ordering and FAQ

    Ask for the price or details:
     - Web:  http://
    Country: *

    Spam protection. How many is SIX times six?

  • How can I order a sample of ER84?
    We either fulfill your order at HW group in Prague, or we pass it down to our distributor in your country.
    (List of HW group distributors).
  • Where can I find product pricing?
    Ask our distributors, or request a quote (by e-mail or by filling out this form).
  • What is the warranty?
    The standard warranty for this product is 2 years, can be extended upon request.
  • Can I pay by credit card?
    Yes, HW group accepts payments by credit card or wire (bank) transfer. However, your card number needs to be manually written down into a form on the received invoice, which is then faxed back to us.
  • How do you ship?
    We work with several shipping companies, and we use FedEx for express deliveries.

  • Is it possible to control the outputs and read the inputs over a WEB interface?
    No, I/O Controller products do not have a built-in web server, all communication takes place over a TELNET-like protocol. If you need a Web interface, use our Poseidon or Damocles products.
  • Is it possible to switch 110/230VAC mains voltage with the output relay?
    No, use our IP Relay ER02a or Poseidon 3468 products.
  • Can I control the product from my own SW application? Where can I find a description of the protocol?
    Yes, use the HWg-SDK examples or see the description in NVT documentation.

>> Online order form

Ordering numbers

OID Description
600 347
I/O Controller HWg-ER84a
I/O Controller ER84a unit only, no power adapter or cables.
600 375
I/O Controller HWg-ER84a SET
Recommended set for getting started with the product. Includes: ER84a, power adapter, cables, CD, etc.

More accessories



I/O Controller ER84a, Telnet Relay, TCP relay outputs, RS-485 to IP, Serial printer to IP, button over IP
M2M serial ethernet, free virtual serial port, Device server with IO, RS-232 printer to Ethernet


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