Basic of CAN
Parameter manual
b maXX
®
1000
Document no. 5.07004.03
Baumüller Nürnberg GmbH
178
B.3
m
Node guarding
Node guarding is the monitoring of the slave by the master. At the same time, the slave can monitor the master
(life guarding).
The master interrogates the slaves at certain intervals by means of remote frames. Remote frames are special
message frames with which it is possible to request data message frames. Remote frames have the same COB
ID as the related data message frame, but present a data length of 0 bytes. The so-called RTR bit in the control
field of the remote message frame serves to differentiate between remote and data message frames (message
frame differentiation takes place normally by means of the COB ID). In the remote frame, the RTR bit is at “1”,
in the data message frame at “0”.
The COB ID results from
700
hex
+ address
, according to the predefined connection set. This COB ID can also
be modified. The object required for this is
100E
hex
.
The guarding time is set in Objects
100C
hex
and 100D
hex
. Within this time, the slave must have received a
guarding request (remote message frame) from the master. Should this not be the case, the life guarding event
occurs in the slave. Through this, the slave switches to the PRE-OPERATIONAL state and the reaction spec-
ified in
Object 6007
hex
is triggered in the controller (drives).
If there is no response from the slave within a certain time, the node guarding event will be triggered in the
master. If no time is set, the slave will respond to every RTR, but without monitoring lifetime.
The current communication state of the slave can be recognized from the response of the slave to a node
guarding request from the master. The response message frame consists of one data byte (see also Node
Guarding Protocol). Field “s” differs according to the communication state. In addition, with two successive
message frames, toggle bit “t” will be changed.
Node guarding is available in all communication phases. The toggle bit is only reset to its default value in the
INITIALIZATION phase. This means that the toggle mechanism is continued also on changing state.
Node guarding is started in the slave after receipt of the first guarding request message frame. From this mo-
ment, the monitoring time parameterized in Objects
100C
hex
and
100D
hex
runs in the slave.
Communication phase
Identifier s
Resulting data with
t = 0
t = 1
PRE-OPERATIONAL
7F
hex
(127)
7F
hex
(127)
FF
hex
(255)
OPERATIONAL
05
hex
(5)
05
hex
85
hex
(133)
STOPPED
04
hex
(4)
04
hex
84
hex
(132)