CAN in Automation (CiA): Network Management

All CANopen devices must support the CANopen network management (NMT) slave state machine. The NMT state machine defines the communication behavior of a CANopen device. The CANopen NMT state machine consists of an Initialization state, a Pre-operational state, an Operational state, and a Stopped state. After power-on or reset, the device enters the Initialization state.

After the device initialization is finished, the device automatically transits to Pre-operational state and indicates this transition by sending the boot-up message. This way the device indicates that it is ready to work. A device that stays in Pre-operational state can start to transmit SYNC-, Time Stamp- or Heartbeat  messages if these services are supported and configured in the right way. In contrast to PDO communication that has to be disabled in this state, the device can communicate via SDO. PDO communication is only possible in the Operational state. During Operational state, the device can use all supported communication objects. A device that was switched to the Stopped state only reacts to received NMT commands. In addition, the device indicates the current NMT state by supporting the error control protocol during Stopped state.