User manual

Chapter 9 Special Features: IA (Industrial Automation) 63
Industrial Automation (IA) uses the Modbus protocol that defines how
devices in an IA environment communicate. It specifies that a controlling
unit, called a master, manages one or more units, called slaves. Only the
master may initiate communication, and slaves may only respond.
Some of the elements of communication between devices that are defined
by the Modbus protocol include:
• The structure of Modbus messages
• How the master requests information from the slave or specifies an
action for the slave to take
• How the slave is to respond
• Addressing conventions
• Handling of many of the other details required for communication to
occur.
Modbus defines two encoding schemes: Modbus ASCII and Modbus RTU.
Each Modbus device uses one or the other.
Designed to function over a serial communication cable, Modbus has been
extended in recent years to function over an Ethernet network using
Modbus/TCP, which defines a method of encapsulating Modbus ASCII or
Modbus RTU messages in IP packets for transport over the network.
The extermely flexible Digi implementation includes support for Modbus
ASCII, Modbus RTU, Modbus/TCP, and two other methods of transport
over a network, TCP socket and UDP socket communication. The
implementation enables multiple network-based masters to concurrently
initiate communication with serial-based slaves using any of the supported
network protocols.
Configuring Industrial Automation with Modbus
1. Click Serial Port > Change profile and select Industrial Automation.
2. Click Apply.
3. Under Profile settings, click change protocol.
4. Select the protocol that best matches your environment (master or
slave) Use the Help button for additonal information.
5. Enter the User defined protocol settings (Start delimiter, end delimiter,
Message timeout, and Process ANSI escape characters) and click
Apply.
6. Click Packet Routing > Add.
7. Enter the packet routing information. Click the Help button for additional
information.
Note: Configure the serial port for the serial communication parameters (baud rate,
data bits, parity and stop bits) required by the connected IA device. If you
configure the port for a slave, you do not have to configure a network-based
master. Communication with the master just works. (If the master is
Chapter 9
Special Features: IA (Industrial
Automation)