Basic Operation
17
Doc.Id. SCM-1200-093
Anybus Communicator for Modbus Plus
Doc.Rev. 3.01
2.3 Subnetwork Protocol
2.3.1 Protocol Modes
The gateway features three distinct modes of operation regarding the subnetwork communication, called
‘Master Mode’, ‘DF1 Master Mode’ and ‘Generic Data Mode’. Note that the protocol mode only spec-
ifies the basic communication model, not the actual subnetwork protocol.
• Master Mode
In this mode, the gateway acts as a master on the subnetwork, and the serial communication takes
place in a query-response fashion. The nodes on the network are not permitted to issue messages
unless they have been addressed by the gateway first.
For more information about this mode, see “Master Mode” on page 18.
• DF1 Master Mode
In this mode, the gateway acts as a master on the subnetwork, using the DF1 protocol. The serial
communication takes place in a query-response fashion. For information about this mode see
“DF1 Protocol Mode” on page 51.
• Generic Data Mode
In this mode, there is no master-slave relationship between the subnetwork nodes and the gate-
way; any node on the subnetwork, including the gateway, may spontaneously produce or con-
sume messages.
For more information about this mode, see “Generic Data Mode” on page 19.
2.3.2 Protocol Building Blocks
The following building blocks are used in Anybus Configuration Manager to describe the subnetwork
communication. How these blocks apply to the three protocol modes will be described later in this doc-
ument.
• Node
A node represents a single device on the subnetwork. Each node can be associated with a
number of transactions, see below.
• Transaction
A ‘transaction’ represents a complete serial telegram, and consists of a number of frame objects
(see below). Each transaction is associated with a set of parameters controlling how and when to
use it on the subnetwork.
• Commands
A ‘command’ is simply a predefined transaction stored in a list in the Anybus Configuration Man-
ager. This simplifies common operations by allowing transactions to be stored and reused.
• Frame Object
‘Frame objects’ are low level entities used to compose a transaction (see above). A frame object
can represent a fixed value (a constant), a range of values (limit objects), a block of data or a cal-
culated checksum.
Summary of Contents for Communicator Modbus plus
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