9 | More about CANopen?
STÖBER
46
09/2019 | ID 442637.01
9.3.4
Error Control Objects – ERROR
To enable monitoring of the NMT states of the individual bus nodes, CANopen offers 2 ERROR CONTROL services, which are
based on periodic message transmission:
node/life guarding and heartbeat. Node/life guarding and heartbeat have the same COB-ID, which means the two control
mechanisms cannot be used simultaneously; that is, you can either enable one of the two services or disable both.
ERROR CONTROL messages have the "NMT_Error_Control" identifier together with the associated node ID.
9.3.4.1
Node/life guarding
Node/life guarding provides mutual communication control of the controller and drive controller.
A controller uses remote requests to query the internal operating state (Operational, Pre-operational, etc.) of all drive
controller connected by the CAN bus. When a remote request is made, a remote frame is sent that contains no data, only
the ID of the desired message. These remote frames are answered from the respective drive controllers by corresponding
data frames. This allows the controller to check whether its own state matches that of the drive controllers. In return, the
drive controllers detect whether the controller is enabled: If the controller does not send any remote frames within a
certain time, the drive controllers assume there is a communication error and trigger corresponding faults.
If the node/life guard mechanism is enabled, the heartbeat service must be disabled.
Guard time
The guard time defines the time interval within which the controller sends remote frames to the drive controllers.
Life time factor
The life time factor indicates how high the number of missing remote frames of the controller has to be before the drive
controllers switch to the Fault state.
Life time
The life time is the product of the life time factor and guard time, i.e. the monitoring time within which the controller sends
remote frames and the drive controllers answers each of these with a data frame. If either the life time factor or the guard
time is set to zero, the life time is automatically disabled.