| ELECTRONIC DATA SHEETS (EDS) |
DeviceNet vendors are required to provide
some type of documentation specifying how their device
is configured. The document may be a set of printed instructions
or some electronic file. At the minimum the vendor must
provide instructions for any external switches and a list
of Class/Instance/Attribute values that control the configuration
of the device. Some vendors create a “configuration
assembly” containing the parameter data. This assembly
provides a single attribute, a single point of reference
where all device parameters can be read and written.
An electronic listing of the Attributes that configure
a DeviceNet device is usually provided by a vendor. These
EDS files sometimes provide little to no information on
the device or they can be very lengthy and complex. The
more extensive EDS files allow configuration tools to
precisely configure the device using text identifiers
for bit values and other very informative text strings.
|
| TYPICAL DEVICENET DEVICES |
| |
| DeviceNet I/O Devices |
Most DeviceNet devices are Slave I/O
devices. A DeviceNet I/O device transfers discrete or
analog I/O points to a DeviceNet Master. DeviceNet I/O
devices come in all shapes and sizes from one or two points
to many points. A lot of I/O devices are non-isolated
and are powered from the network while others use isolated
outputs.
|
| DeviceNet Masters |
DeviceNet Master Devices are usually
Programmable Controllers or Personal Computers. DeviceNet
Master Devices allocated DeviceNet slaves and transfer
data between the Master and it’s Slaves.
|
| DeviceNet Gateways |
DeviceNet Gateways convert data from
another protocol to DeviceNet. Modbus DeviceNet gateways
for example convert Modbus devices to DeviceNet devices.
ASCII DeviceNet gateways take ASCII data and convert it
to Modbus. There are innumerable protocol converters for
DeviceNet.
The difficult issue for a DeviceNet gateway is mapping
data in the other protocol to the object structure of
DeviceNet. For example, the Modbus protocol represents
its data as a series of 16-bit integers while CIP represents
data as attributes that are part of objects. A DeviceNet
gateway must allow some method to convert the data in
its native Modbus, ASCII or other format to the object-based
structure of DeviceNet. |
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