ICON
I/O Overview
Introduction
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.
ICONIO Board
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. |
