Functional Description
2
ekr 500 digital Unit Touch – CANopen User Gateway 11/67
2.3.1 Service Data Objects
The Service Data Objects (SDOs) enable access to the object
dictionary of the controller. Service Data Objects are used for the
parameterization of the web guiding controller and for status
requests.
The SDO access is a confirmed access method. Using this type of
access, the web guiding controller confirms each parameter
access of the customer control system.
Order from control system
Confirmation from controller
Customer
control system
Fig.2: SDO access
An SDO access always starts from the higher-level control system
(host), which sends to the web guiding controller either a write
command in order to change a parameter of the object dictionary
or a read command in order to read out a parameter. For each
command, the host receives a response from the controller. This
answer either contains the readout value or – in the case of a
write command – serves as a confirmation.
Each message sent on the CAN bus includes a kind of address used
to define the bus participant the message is addressed to. This
number is called the identifier. The lower the value of the identi-
fier, the higher is the priority of the message. The identifier con-
sists of the base 600h and the node number of the controller.
The structure of the commands and answers depends on the data
type of the object to be read or written, because 1, 2 or 4 data
bytes have to be sent or received.