NMT

The network management (NMT) protocols provide services for network initialization, error control and device status control. NMT objects are used for executing NMT services. The NMT follows a master-slave structure and therefore requires that one CANopen device in the network fulfils the function of the NMT master. All other CANopen devices are regarded as NMT slaves. An NMT slave is uniquely identified in the network by its Node-ID, a value in the range of 1 to 127.

The NMT state machine defines the communication status for CANopen devices.

NMT state initialization

The initialization state could be divided into three sub-states that are executed in a sequential way: Initializing (performs the basic CANopen initializations), Reset application (in where all manufacturer-specific and standardized profile area parameters are set) and Reset communication (where the communication profile and parameters are set). 
At the end of initialization state the device sends a boot-up message and goes directly to Pre-Operational state.

NMT state pre-operational

In Pre-Operational state, the communication using SDO messages is possible. PDO message are not yet defined and therefore communication using these message is not allowed. The device will pass to Operational message after receiving a NMT start node command.
Normally the master puts a node in Pre-Operational state during the set-up and configuration of device parameters.

NMT state operational

In Operational state all kind of messages are active, even PDO messages.

NMT state stopped

When entering in Stopped state, the device is forced to stop all communications with the exception of the NMT commands. (Node Guarding & Life Guarding).

NMT states and communication object relation

Following table shows the relation between communication states and communication objects. Services on the listed communication objects may only be executed if the devices involved in the communication are in the appropriate communication states 

NMT services

The structure of each NMT service command is as follows:

The possible NMT services commands are the followings:

Example of NTM services:

NMT error control

Protocol node guarding

The NMT Master can monitor the communication status of each node using the Node Guarding protocol.
During node guarding, a controller is polled periodically and is expected to respond with its communication state within a pre-defined time frame. Note that responses indicating an acceptable state will alternate between two different values due to a toggle bit in the returned value. If there is no response, or an unacceptable state occurs, the NMT master could report an error to its host application. 
The NMT master sends a node guarding request using the following a Remote Frame message:

The NMT slave will generate a node guarding answer using the following message:

Note that the slave answers toggling a bit between consecutive responses. The value of the toggle bit of the first response after the guarding protocol becomes actives is zero. 
The state of the heartbeat producer could be one of the followings:

Example of NMT Node guarding:

Protocol heartbeat

The heartbeat protocol defines an error control service without need for remote frame. A heartbeat producer (in this scope a controller) transmits a Heartbeat message cyclically. Transmit cycle of heartbeat message could be configured using the object Producer heartbeat time (0x1017). If the Heartbeat is not received by the consumer (in this scope a master) within an expected period of time (normally specified as Consumer heartbeat time) it could report an error to its host application. 
Devices based on emcl are only heartbeat producers. 
The heartbeat message generated by the producer will be as follows:

The state of the heartbeat producer could be one of the followings:

Example of NMT heartbeat:

Protocol lifeguarding

In Life guarding protocol the NMT slave monitors the status of the NMT master. This protocol utilizes the objects Guard time (0x100C) and Life time factor (0x100D) to determine a "Lifetime" for each NMT slave (Lifetime = Guard Time * Life Time Factor). If a node does not receive a Node Guard message within its Lifetime, the node assumes communication with the host is lost sends an emergency message and performs a fault reaction. Each node may have a different Lifetime. 

Example of NMT life guarding:

Note: to start the Life Guarding protocol, both Guard Time and Life Time Factor need to be different than 0, and a first CAN remote frame without data needs to be send to each node.

Protocol boot-up

An NMT slave issues the Boot-up message to indicate to the NMT-Master that it has entered the state Pre-operational from state Inititalising.
Example of NMT Boot-up: