Short description of CANopen
D301087 0308 - BL20 CANopen2-6
Special Function Objects
CANopen also defines three specific protocols for synchronization,
emergency indication, and time-stamp transmission.
Synchronization object (Sync)
The Sync Object is broadcast periodically by the Sync Producer.
The time period between Sync messages is defined by the
Communication Cycle Period, which may be reset by a configu-
ration tool to the application devices during the boot-up
process. There can be a time jitter in transmission by the Sync
Producer due to some other objects with higher prior identifiers
or by one frame being transmitted just before the Sync message.
The Sync message is mapped to a single CAN frame with the
identifier 128 by default. The Sync message does not carry any
data.
Emergency object (Emcy)
The Emergency message is triggered by the occurrence of a
device internal error situation and are transmitted from an Emer-
gency producer on the concerned application device. This
makes them suitable for interrupt type error alerts. An Emer-
gency message is transmitted only once per ‘error event’. As
long as no new errors occurs on a device, no further Emergency
message can be transmitted. Zero or more Emergency
consumers may receive these. The reaction of the Emergency
consumer is application-specific. CANopen defines several
Emergency Error Codes to be transmitted in the Emergency
message, which is a single CAN frame with 8 data byte.
Time stamp object (Time)
By means of Time-Stamp, a common time frame reference is
provided to application devices. It contains a value of the type
Time-of-Day. This object transmission follows the producer/
consumer push model. The associated CAN frame has the pre-
defined identifier 256 and a data field of 6-byte length.
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