BECKHOFF CX2100­09x4 - Manual (Page 19)

Product overview
CoE interface – parameter management in the EtherCAT system
Many different devices are used in an automation environment. These devices can be used separately or
together in a group on a bus system. Such devices can be controllers, shaft encoders, servo drives, motors,
I/O modules or sensors among other things. Depending upon complexity, such a device must be
parameterizable/adjustable for the respective requirement. Parameterization is perhaps not necessary in the
case of a simple digital 24 V input with a fixed switching threshold and delay; in the case of a shaft encoder,
however, it will not be possible to do without it (e.g. number of lines, absolute or relative, data format, etc.)
On top of that it can be of interest to store data in the device during production or operation. The
manufacturer could store production data such as device name, serial number, firmware version, calibration
data or date of manufacture, if necessary provided with protection against access or amendment. The user
could store user calibration data and the application­specific settings in the device.
In order to create a user­friendly interface for device operation, different organizations have created various
standards in which the following are defined: the available device classes (e.g.: ‘rotary encoder’, ‘analog
input module’ class), the parameters that each representative of such a class has (obligatory and optional
elements), the locations where these parameters can be found and the mechanism with which they are to be
changed. EtherCAT follows the so called CoE standard here: Can­Application­protocol­over­EtherCAT.
Can­over­EtherCAT
The CiA organization (CAN in Automation) pursues among other things the goal of creating order and
exchangeability between devices of the same type by the standardization of device descriptions. For this
purpose so­called profiles are defined, which conclusively describe the changeable and unchangeable
parameters of a device. Such a parameter encompasses at least the following characteristics:
• Index number – for the unambiguous identification of all parameters. The index number is divided into
a main index and a subindex in order to mark and arrange associated parameters.
­ Main index
­ Subindex, (offset by a colon “:”)
• Official name – in the form of an understandable, self­descriptive text
• Specification of changeability, e.g. whether it can only be read or can also be written
• A value – depending upon the parameter the value can be a text, a number or another parameter
index.
Example: the parameter ‘Vendor ID’ might have the index number 4120:01 and the numerical value ‘2’ as the
ID of a Beckhoff device.
Since hexadecimal values are favored in the machine environment, the parameter is represented from the
user’s point of view as if it had the RO property (read only), because the vendor ID should not be changed by
the user.
Such a list of parameters, the whole of the device­specific CoE directory, can become very extensive. The
first entries of a Beckhoff EL3152 analog input terminal appear as follows in the TwinCAT System Manager:
The index numbers are specified in the profile; they begin in EtherCAT with x1000, because the underlying
entries do not have to be displayed.
CoE directory – availability
An EtherCAT device can have a CoE directory, but does not need to have one. Simple slaves need no
parameter directory or do not have the controller required for administration. On the other hand, the
EtherCAT master (like TwinCAT) as a software EtherCAT device can also manage a CoE directory.
If present, the CoE directory is in operation from the PREOP state.
The object directory can be read via the SDO information service (Service Data Objects).
CoE directory – localization in the EtherCAT Slave
The CoE directory as a parameter system must be administrated in the device in the firmware (FW) in the
local controller. This is the so­called online directory, because it is only available to the user if the EtherCAT
slave is in operation with operating voltage supplied and, if applicable, can be manipulated via EtherCAT
communication.
CX2100­09x4 19 Version 1.1