WIKA D-21-9 - Manual (Page 43)

D-20-9 / D-21-9 GB
WIKA Additional Instructions Pressure Transmitter with CANopen Interface D-20-9 / D-21-9 43
Node Guarding Protocol
This protocol is used to detect remote errors in the network. Each NMT Slave uses one remote COB for the
Node Guarding Protocol. This protocol implements the provider initiated Error Control services.
s: the state of the NMT Slave
4: STOPPED
5: OPERATIONAL
127: PRE-OPERATIONAL
t: toggle bit. The value of this bit must alternate between two consecutive responses from the NMT Slave. The
value of the toggle-bit of the first response after the Guarding Protocol becomes active, is 0. The Toggle Bit in
the guarding protocol is only reset to 0 when reset_communication is passed (no other change of state resets
the toggle bit). If a response is received with the same value of the toggle-bit as in the preceding response
then the new response is handled as if it was not received.
The NMT Master polls each NMT Slave at regular time intervals. This time-interval is called the guard time
and may be different for each NMT Slave. The response of the NMT Slave contains the state of that NMT
Slave. The node life time is given by the guard time multiplied by the life time factor. The node life time can be
different for each NMT Slave. If the NMT Slave has not been polled during its life time, a remote node error is
indicated through the 'Life Guarding Event' service.
A remote node error is indicated through the 'Node guarding event' service if:
−
The remote transmit request is not confirmed within the node life time
−
The reported NMT slave state does not match the expected state
If it has been indicated that a remote error has occurred and the errors in the guarding protocol have
disappeared, it will be indicated that the remote error has been resolved through the 'Node Guarding Event'
and 'Life Guarding Event' services.
For the guard time and the life time factor there are default values specified at the appropriate Object
Dictionary entries.