BL20 - Communication in CANopen
D301087 0308 - BL20 CANopen4-14
The node answers the telegram sent out by the network manager
within the preset time (Guard time) in the "Operational" state, with
the data contents 5. The gateway answers the next polling query
with the contents 133. The following response from the gateway is
with 5 again, and so on. This means that the gateway changes the
state of the most significant bit after every query (i.e. the bit is
toggled).
If the node is in the "Pre-Operational" state, then the value of the
data contents of the response telegram toggles between 127 and
255. If the node is in the "Stop" state, the value toggles between 4
and 132.
If there is no query from the network manager within the preset time,
then the gateway changes to the state "Guard Fail". If output
modules are fitted in the BL20 station, then their outputs will be put
into defined states, depending on the objects "Error mode output"
and "Error state output", or will retain the last state that was
received. Any RxPDOs that are received will still be processed and
output again. If the Guarding starts up again, the BL20 gateway
leaves the "Guard Fail" state, but remains in the Pre-Operational
state.
A "Start Node" command must be generated by the network
manager in order to restart the BL20 gateway (see CiA DS-301).
If the setting is Guard time = 0, then "passive Guarding" will occur.
This means that the gateway answers the Guard Remote frames,
without starting its own internal Guard timer and without changing
into the "Guard fail" state.
As an alternative to Node-/Life-Guarding, the Heartbeat mechanism
newly introduced with DS301 V4.0 is supported, which, unlike
Guarding, does not require Remote frames.
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