D8 Series User’s Guide
Chapter 3: Communicating by DeviceNet
47
Master/Slave Connections
The D8 supports the
Predefined Master/Slave Connection Set
, which calls for the utilization of an
Explicit Messaging Connection to manually create and configure Connection Objects within each
connection end-point. These Connections are referred to collectively as the
Predefined Master/Slave
Connection Set
.
The
master
is the device that gathers and distributes I/O data for the process controller.
Slaves
are
the devices from which the master gathers I/O data and to which the master distributes I/O data.
The master “owns” the slaves whose node addresses appear in its scan list. To determine which
slaves it will communicate with, the master examines its scan list and sends commands accordingly.
Except for the Duplicate MAC ID Check, a slave cannot initiate any communication before being told
by the master to do so.
Addressing
All data is referenced using a four-part definition: Node (MAC ID) + Class + In Attribute.
Table 3.2
– Address Components
ADDRESS COMPONENT
RANGE
Node Address (MAC ID)
[0 to 63]
Class ID
[1 to 255]
Instance ID
[0 to 255]
Attribute ID
[1 to 255]
Data Types
The descriptions of attributes in the following sections include the data type for each. Table 3.3 lists
and describes these data types.
Table 3.3
– Elementary Data Types
TYPE
DESCRIPTION
BOOL
Logical Boolean (TRUE or FALSE)
BYTE
Bit string (8 bits)
EPATH
DeviceNet™ path segments
INT
Signed integer (16 bits)
SHORT_STRING
Character string (1 byte per character, 1 byte length indicator
UDINT
Unsigned double integer (32 bits)
UINT
Unsigned integer (16 bits)
USINT
Unsigned short integer (8 bits)
WORD
Bit string (16 bits)
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