Communication via CAN bus (CANopen)
AP10
Date: 28.02.2022 Art. No. 86853 Mod. status 37/22 Page 28 of 78
5.5.3 Heartbeat
The master monitors the status of the slave device via the Heartbeat protocol. While doing
this, the unit sends cyclically its NMT status. The AP10 is a heartbeat producer, it does not
receive nor process heartbeat protocols. The cycle time of the heartbeat message is set via
object 1017h. The heartbeat protocol is inactivated if the cycle time is 0.
The heartbeat message consists of the COB-ID and an additional byte, which is used to store
the current NMT status.
NMT status:
4: STOPPED
5: OPERATIONAL
127: PRE-OPERATIONAL
The identifier of the heartbeat protocol is permanently set to 700h + Node-ID and cannot be
changed. Sending of a Node Guard message is possible in the "OPERATIONAL",
"PREOPERATIONAL" or "STOPPED" NMT statuses.
5.5.4 External heartbeat
In addition to the function described under Heartbeat, the NMT status can be controlled via
the external heartbeat. In this case, a value corresponding to an interval in ms is entered in
object 5F09h sub-index 1. If the devices receive no external heartbeat message during this
interval, the display will switch over to Pre-Operational status. The type of message to be
interpreted as external heartbeat is set in object 5F09h sub-index 2. The value 0 means that
the timer is triggered when receiving an RPDO (set point). With value 1, the timer is triggered
when receiving a SYNC (see object 5F09h: External Heartbeat timer and external Heartbeat
source).
5.5.5 Guarding Bit
There is a guarding bit in the control word, which serves for monitoring communication or the
NMT state of the device, respectively. When receiving the control word, the content of this bit
will be copied into the guarding bit of the status word and output with the next TPDO. Thus,
by shifting the bit in the control word, the superordinate control can verify without additional
data traffic that process data exchange is in operation. This function is especially helpful
when a gateway (converter from CANopen to superordinate fieldbus) is used.
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