Western Reserve Controls, Inc.
1782-JDO User’s Manual
PRELIMINARY
25
6.4 Common DeviceNet services
The common DeviceNet services are available through many of the common configuration
tools. However, each configuration tool may implement these differently. It may be easier if
you use this section in conjunction with any files or documentation that was included with
your DeviceNet configuration tools while going over this section.
DeviceNet is divided into logical functional blocks called objects, which provide services that
allow for control over the hardware and routines that those objects contain. To allow for
multiple similar functions, the objects are built of multiple instances that the services of the
objects act upon. A class service acts upon the entire object, allowing one service to be
enacted on all of the instances. This saves time, effort and network bandwidth.
The common services are a common set of services that have been provided in most or all of
the objects to allow for common functionality in creating, deleting, getting, setting and
resetting the variables of the different classes and instances. We will describe two of the
services here: get and set.
The get and set services have a common format for specifying what object, instance, attribute
and service that the command is specifying. In order of first to last, DeviceNet specifies
service, class, instance, attribute and data. The data is always little-endian (low byte
precedes high order byte), and the others are all one byte in length on the JDO. Note that
the get service has no data.
The get service gets data from an attribute of a class or class instance. The service number
of this request is 14 (E
hex
). The class instance and attribute are all defined by which variable
you want to get. The response from a get command takes on the form: service, value. The
value will be little-endian and can be of variable length and bounds based on the definition of
the attribute. The service will be reported as the get service with the highest bit set to
indicate a response.
The set service sets data from an attribute of a class or class instance. The service number
of this request is 16 (10
hex
). The class instance and attribute are all defined by which variable
you want to set. The value is little endian, and the size is defined by the attribute that you are
setting. The response from a set command only echoes the service. The service will be
reported as the set service with the highest bit set to indicate a response.
An error response will have the service set to 94
hex
. This response will be followed by a two-
byte error code, defining the type of fault. For a detailed list of error codes, connect to the
ODVA web site at
www.odva.org
.