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1. Introduction
Different Connection Types
There are two messaging connections: I/O messaging connection and explicit messaging
connection. The I/O messaging connection includes polling, strobe, cyclic, and change of
state. I/O messaging connections are explained below:
Polling: First, a master device sends output data to a slave device and then the slave device
responds. Data is normally exchanged in every communication cycle. The
communication frequency can be changed by setting. This connection type is the
most often used.
Strobe: First, a master device requests slave devices to send data with multicast messages,
and then, each slave device responds separately.
Data from many sensors on the system can be effectively gathered. When the master
does not receive responses from all requested slave devices, a timeout error occurs.
Change Of State:
A device sends data whenever it changes. Signals for device diagnosis are sent
regularly in the background. This connection type is useful for remedying DeviceNet
communication traffic.
Cyclic: A slave device transfers data regularly according to its internal timer. This
connection type is typically used for communicating with a temperature controller.
The data transfer frequency is defined by master configuration.
For Change of State and Cyclic, you can disable the ACK that is for verifying that
communication is completed. Never disable ACK, since communication errors cannot be
detected.
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NOTE
Functions of Master
The Master device gathers and controls all nodes on one network.
A DeviceNet master can control up to 64 nodes (max. 2 kbytes) on one network.
A PLC is typically configured as a master and controls all nodes in factory automation system,
but EPSON RC+ is also capable of being a master.
DeviceNet network configuration is specified by configuration management software. This
software is normally provided by a master device manufacturer. The configuration
management software determines parameters for each slave device via an Electronic Data
Sheet (EDS).
Available connection types are Polling, Strove, Cyclic, Change Of State, and explicit
messaging.
Available baud rates are 125 kbps, 250 kbps, and 500 kbps.
Functions of Slave
A slave can exchange data with a master device.
The configuration management software identifies parameters of each slave device via
Electronic Data Sheet (EDS) where the parameters are registered.
Available connection types are Polling, Strobe, Cyclic, and Change of State.
Available baud rates are 125 kbps, 250 kbps, and 500 kbps.
Fieldbus I/O Rev.6 3