Home of the ICON - Instrumentation and Control Over Networks Last updated April 1, 2007

     ICONIO Board
     1-Wire I/O Devices

     ICONIO Card Installation
     ICONIO Programming

     Basic 1-Wire Installation

     2 Chan Counter (OWCTR2)

     2 Chan A-D (OWAD2)

     4 Chan A-D (OWAD4)

     1 Chan Pot Out (OWPOT1)

     Dry Contact (OWRELAY4)

     Connections (OWCONNECT)

     Temperature (OWT)

     Relative Humidty (OWTRH)

     Light (OWL)

     Weather Station (OWWEATHER) 


     Phone: (406) 599-1053

ICON I/O Overview

The ICONIO board is a serial RTU Modbus slave unit that allows the ICON Controller or other standard serial Modbus master device to control selected Dallas Semiconductor 1-wire devices using standard 16 bit Modbus registers.

The ICONIO board "looks" like a Modbus RTU slave device to the Modbus controller. Modbus is a serial protocol originally developed by the industrial control manufacturer "Modicon". The Modbus control protocol has been the defacto open standard for industrial controls for over 20 years. Modbus is popular because the specification is published for anyone to use, it is simple and reasonably powerful. Each Modbus node must have a unique unit address in the range of 1 to 255.

The actual I/O is connected to the 1-wire devices which include counter/frequency inputs, analog to digital converter inputs, digital inputs, temperature, relative humidity, light, digital outputs (including mechanical and solid state relays) and digital to analog converter outputs.


There are two versions of the ICONIO board - ICONIO-LOCAL and ICONIO-REMOTE. The ICONIO-LOCAL is a special configuration that connects to the ICON Controller board. The ICONIO-REMOTE is used for additional I/O capability when using the ICON Controller or in all other cases when using third party Modbus master devices.

The ICONIO board can be configured two ways. The first way provides one RS232 interface to be connected to the local Modbus master and a second 2-wire RS485 interface to connect to up to 31 additional 2-wire RS485 Modbus slave devices. The second configuration contains just the 2-wire RS485 interface.

The RS485 bus may be up to 4000 feet from end to end. A Cat 5 cable connects the second ICONIO board to the first. From here a second Cat 5 cable connects the third ICONIO board to the second ICONIO board. This daisy chained Cat 5 cable continues to the last ICONIO board.

Each ICONIO board contains four Dallas Semiconductor 1-wire device busses. A Cat 5 cable connects the ICONIO board to the first 1-wire device. A second Cat 5 cable connects the first 1-wire device to the second 1-wire device. The second connects to the third, etc. This daisy chained Cat 5 cable continues to the last device. Because each bus is daisy chained, the ICON has four separate 1-wire busses that can each go up to 500 feet or more in a different direction.

This connection scheme can be seen graphically in Figure 2.

As Modbus is used for the ICONIO board, there is just one data type called a register which is a 16 bit unsigned integer. Therefore all data values are in the range of 0 to 65535. The ICONIO board has three types of Modbus registers, the configuration registers, the data input registers and the data output registers.

You write to the Modbus configuration registers to set the 1-wire device types, node addresses and bus numbers. The ICONIO board scans the 1-wire devices writing inputs such as temperature to the Modbus input registers and sending the Modbus output register values to 1-wire output devices.

Modbus Interface Specifications

  • Serial Modbus RTU slave 
  • Baud rate of 9600 or 19200 switch selectable 
  • Unit address of 1 to 255 switch selectable 
  • RS232 or 2-wire RS485 
  • RS485 supports up to 32 nodes on a cable length up to 4000 feet 
  • Supports Modbus commands 3, 4, 6 and 16 
  • Three sets of Modbus registers, data input, data output and configuration 
  • All 1-wire sensor data values mapped to a data range of 0 to 65534 (binary) 
  • A data reading of 65535 indicates a 1-wire device missing or failure error 
1-Wire Interface Specifications
  • Four separate Dallas Semiconductor 1-wire device busses 
  • Each bus terminated on a four position screw lug connector with the 1-wire signal, 1-wire common, +5V and +5V common 
  • Supports 1-wire bus lengths to 500 feet 
  • Supports DS18S20 temperature probe, DS2450 4 channel A-D input or digital output, DS2423 2 channel event counter/frequency measurement, DS2438 temperature, Relative Humidity and two channel A-D input and DS2890 1 channel analog output 
  • Above 1-wire devices can be purchased from our company pre-packaged for monitoring and control applications 
  • Modbus configuration registers allow the configuration of 1-wire device type, ID, bus power type (continuous or 1-wire powered), read timing and number of retries 
  • Configuration of read timing allows 1-wire devices to be placed anywhere along a 1-wire bus up to 500 feet or more 
General Specifications
  • Contained on small PC board 4.00 X 5.75 inches 
  • DIN rail or standoff mounted (also available in a 10 X 10 inch metal enclosure including step down AC transformer 
  • Power 9 to 24 VAC or VDC (low power all CMOS design allows solar panel with battery operation) 
  • Temperature range 0-50C (32-122F) 
  • Humidity 5-95% non-condensing 
1-wire I/O devices

The integrated semiconductor manufacturer, "Dallas Semiconductor", manufactures a line of low cost sensors and actuators that are ideal for low cost instrumentation and control. These devices include temperature, Analog to Digital (A-D) converters for measuring voltage and on/off digital status, event pulse counting (and frequency measurement), digital on/off control (for controlling relays) and potentiometer control (Digital to Analog D-A converter) output.

A family of 1-wire products are pre-packaged for easy use. (Refer to the manual links at the top left of this page for information on the available interfaces.) These boards include the appropriate 1-wire IC, connectors and lightning and ESD protection and can be mounted to DIN rail fasteners, placed inside Carlon (or similar) plastic boxes (available at Home Depot) or placed inside 1.25" PVC pipe with end caps. The PVC enclosure creates a very low cost, water proof housing for use in green houses, outdoors or other wet locations.

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