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Implicit Communication

Implicit communication can be used in the EtherNet/IP Device Service. It is used for time-critical situations. To be as efficient as possible and to reduce bit size, implicit messaging copies data with minimal additional information.

Implicit communication is sometimes called Input/Output (I/O) messaging due to its common usage between controllers and remote I/O devices. For this, implicit communication uses Input (T2O) and Output (O2T) assemblies.

Implicit Device Profile

Implicit communication over EtherNet/IP requires specific attributes to be set within resources in the device profile. These can be found below.

Initialization Resources

Implicit communication settings must be configured in order to use implicit device resources. These configuration resources are loaded when the device service initializes.

O2T & T2O Setting Attributes

O2T and T2O settings must be configured if either is used:

Attribute Description Valid Values
type The type of the settings resource.
Used by the device service to identify the resource type
  • O2TSettings
  • T2OSettings
assemblyID The output assembly instance ID 0 to 65536
includeHeader32bit A flag that defines whether to include a 32-bit header, which includes a run/idle notification
  • true
  • false
size Defines the output assembly size in bytes 0 to 2000

Note

T2O and O2T settings resources cannot be used for read-write operations

Configuration Settings Attributes

This resource is optional and is dependent on the Ethernet/IP device being used.

Attribute Name Description Valid Values
type Configuration Settings Resource Identifier, used by the device service to determine the resource type ConfigSettings
assemblyID Config assembly instance ID 0 to 65535
size Config assembly size in bytes 0 to 400

Note

Configuration settings resources cannot be used for read-write operations

Communication Device Resources

Note

The following resource can only be used if the implicit initialization resources have been set up.

Implicit Communication Device Attributes

T2O and O2T assemblies contain many values which are combined into byte arrays. Due to this, information on each resource must be included to identify the bit and byte operations needed to extract the correct value.

Use the attributes provided below in device resources to extract O2T and T2O values.

Attribute Description Valid Values
type Informs the device service whether it is a T2O or O2T resource
  • T20
  • O2T
offsetBytes Byte offset within the T2O or O2T data 0 to 2000
offsetBits Bit offset within the O2T or T2O data 0 to 7
bitLength Only used for 2 data types:
  • Uint8 (optional)
  • Uint8Array (requirement)
Specifies the length of the value in bits
For data type:
  • Uint8: 1 to 8
  • Uint8Array: 1 to 2000

Note

The maximum supported size of implicit data is 2000 bytes per device.

Implicit Protocol Properties

O2T Protocol Properties

The following O2T protocol properties are required if there is an O2TSettings device resource in the device profile:

Property Description Valid Values
ConnectionType Defines whether data is communicated using peer-to-peer or multicast

Set to p2p to communicate using peer-to-peer
Set to mcast to react in a broadcast way
  • p2p
  • mcast
RPI The Requested Packet Interval, which is the interval in which data is exchanged Interval in milliseconds
Priority Defines the priority in which the implicit data exchange is treated
  • low
  • high
  • scheduled
  • urgent
Ownership Defines the exclusivity of the data on the target If not set to exclusive, other scanners can also establish an implicit connection to the device
  • exclusive
  • inputonly
  • listenonly

T2O Protocol Properties

The following T2O protocol properties are required if there is a T2OSettings device resource in the device profile:

Property Description Valid Values
ConnectionType Defines whether data is communicated using peer-to-peer or multicast

Set to p2p to communicate using peer-to-peer
Set to mcast to react in a broadcast way
  • p2p
  • mcast
RPI The requested packet interval, which is the interval in which data is exchanged Interval in milliseconds
Priority Defines the priority in which the implicit data exchange is treated
  • low
  • high
  • scheduled
  • urgent
Ownership Defines the exclusivity of the data on the target If not set to exclusive, other scanners can also establish an implicit connection to the device
  • exclusive
  • inputonly
  • listenonly