Festo Электромотор MTR-DCI - Manual (Page 28)

1. System overview
1-6
Festo P.BE-MTR-DCI-CO-EN en 1209a
1.2 Field bus communication
1.2.1 Data exchange in CANopen
CANopen devices have an object directory which makes all
important slave parameters accessible in a standardized
manner. A CANopen system is essentially configured by
accessing the objects in the object directory of the individual
stations. The data exchange in CANopen is in the form of tele-
grams with which the work data is transmitted. A distinction
is made between Service Data Objects (SDO), which are used
for transmitting service data from and to the object directory,
and between Process Data Objects (PDO), which serve for the
fast transfer of current process states. In addition, telegrams
are defined for the network management and the fault mess-
ages.
SDO With SDOs you can access all entries in the Object Directory.
The relevant Object Directory entries can be addressed with
the index and subindex of the entry. SDOs are used mainly for
transmitting acyclic data, e. g. for initializing during the boot
procedure. Within an SDO only one object can be accessed. A
reply is always sent to an SDO: A pair of CAN telegrams per
object are transmitted.
PDO PDOs are in principle a grouping of objects (variables or para-
meters) from the Object Directory. Maximum 8 bytes from
different objects can be sent together in a PDO, i. e. the ob-
jects are mapped in the PDO. Process Data Objects can be
transmitted event-controlled, synchronous to a system pulse
sequence or on demand. PDOs are transmitted by simple
CAN messages and are suitable for transmitting cyclic data.