Festo SEC-AC-305-CO, Manual

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4. Access methods/SDO access
4−23
Festo P.BE−SEC−AC−CO−E N en 0802a
4.6 Node−Guarding
The servo controller and the superimposed control are super
vising each other with the node guarding. If node guarding is
activated in the servo controller the superimposed control
has to send messages to the servo controller cyclically. The
servo controller on its side has to answer these messages. If
the cyclical message of the superimposed control does not
arrive within a defined period the servo controller changes
into the error status (display: 24), deactivates the power
stage and sends an emergency message with the error code
8120h.
The permissible period between two messages is determined
by the product of the object
guard_time (100C
h
) and of the
object life_time_factor (100D
h
) . As these two objects are
evaluated in the servo controller only together as a product it
is always possible to set the object life_time_factor (100D
h
)
to one. Then the maximum time interval can be adjusted di
rectly by the object guard_time (100C
h
).
Usually the messages sent by the superimposed control only
consist of remote frames. The CAN controller used in the
servo controller only supports this kind of message telegrams
insufficiently. Therefore normal messages are used instead.
The superimposed control sends messages to the servo con
troller without useful data. The servo controller responds by a
byte which contains the toggle−bit and the
NMT state (see
chapter 4.7 Network management (NMT service)):
Structure of the response of the servo controller:
node guarding telegramm
700
h
+node number Togglebit NMT−State