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44 Fieldbus interface
3 Basics IL•1F CANopen DS301
0198441113586, V2.01, 11.2008
3.5 Synchronization
The synchronization object SYNC controls the synchronous exchange
of messages between network devices for purposes such as the simul-
taneous start of multiple drives.
The data exchange conforms to the producer-consumer relationship.
The SYNC object is transmitted to all devices by a network device and
can be evaluated by all devices that support synchronous PDOs.
Figure 3.25 SYNC message
Time values for synchronization Two time values define the behavior of synchronous data transmission:
• The cycle time specifies the time intervals between 2 SYNC mes-
sages. It is set with the object Communication cycle
period(1006
h
).
• The synchronous time window specifies the time span during which
the synchronous PDO messages must be received and trnasmitted.
The time window is defined with the object Synchronous window
length (1007
h
).
Figure 3.26 Synchronization times
Synchronous data transmission From the perspective of a SYNC recipient, in one time window the status
data is transmitted first in a T_PDO, then new control data is received via
an R_PDO. However, the control data is only processed when the next
SYNC message is received. The SYNC object itself does not transmit
data.
SYNC-Consumer
SYNC-Consumer
SYNC- Producer
COB-ID
CAN
SYNC-Consumer
SYNC
SYNC
cycle time
synchronous
time window
T_PDO (status)
R_PDO (controller)
process
R_PDO data
CAN-Bus