BECKHOFF FC5101 - Manual (Page 35)

Eiserstraße 5 / D-33415 Verl / Telefon 05246/963-0 / Telefax 05246/963-149
35
5. CANopen Communication
NMT
Simple Boot-Up
CANopen allows the distributed network to boot in a very simple way. After initialisation, the modules are auto-
matically in the Pre-Operational state. In this state it is already possible to access the object directory using
service data objects (SDOs) with default identifiers, so that the modules can be configured. Since default set-
tings exist for all the entries in the object directory, it is in most cases possible to omit any explicit configuration.
Only one CAN message is then required to start the module: Start_Remote_Node: Identifier 0, two data bytes:
0x01, 0x00. It switches the node into the Operational state.
Network Status
The states and the state transitions involved as CANopen boots up can be seen from the state diagram:
Pre-Operational
After initialisation the bus coupler goes automatically (i.e. without the need for any external command) into the
Pre-Operational state. In this state it can be configured, since the service data objects (SDOs) are already ac-
tive. The process data objects, on the other hand, are still locked.
Operational
In the Operational state the process data objects are also active.
If external influences (such as a CAN error, or absence of output voltage) or internal influences (such as a K-
Bus error) mean that it is no longer possible for the bus coupler to set outputs, to read inputs or to communi-
cate, it attempts to send an appropriate emergency message, goes into the fault state, and thus returns to the
Pre-Operational state. In this way the NMT status machine in the network master can also immediately detect
fatal errors.
Stopped
In the Stopped state (formerly: Prepared) data communication with the coupler is no longer possible - only NMT
messages are received. The outputs go into the fault state.