CANopen Programmer's Manual - Maccon.de

2: Network Management CANopen Programmer’s Manual
Device Monitoring
Monitoring Protocols
In addition to controlling state machines, NMT messages provide services for monitoring devices
on the network. Monitoring services use one of two protocols: heartbeat and node guarding.
Heartbeat Protocol
The heartbeat protocol allows the network manager application to detect problems with a device
or its network connection. The CANopen master configures the device to periodically transmit a
heartbeat message indicating the device’s current state (pre-operational, operational, or stopped).
The network manager monitors the heartbeat messages. Failure to receive a node’s heartbeat
messages indicates a problem with the device or its connection to the network.
Node-guarding Protocol
The node-guarding protocol is similar to the heartbeat, but it allows both the device and the
network manager to monitor the connection between them. The network manager configures the
device (node) to expect node-guarding messages at some interval. The network manager then
sends a message to the configured device at that frequency, and the device responds with a
node-guarding message. This allows both the network manager and the device to identify a
network failure if the guarding messages stop.
SYNC and High-resolution Time Stamp Messages
The SYNC message is a standard CANopen message used to synchronize multiple devices and
to trigger the synchronous transmission of PDOs.
In addition, to allow more accurate synchronization of device clocks, Copley Controls CANopen
amplifiers use the optional high-resolution time stamp message specified in the Communication
Profile.
Normally, a single device produces both the SYNC message and the high-resolution time stamp
message. Copley amplifiers can produce the SYNC and high-resolution time stamp messages.
We recommend using an amplifier as the master sync generator. This assures greater timing
accuracy and allows the amplifier PVT segment buffer to be filled with the minimum number of
PVT segments at all times during operation.
Time Stamp PDOs
The device designated as the time stamp producer should have a transmit PDO mapped for the
high-resolution time stamp message. This PDO should be configured for synchronous
transmission, based on the SYNC message. We recommend sending this message approximately
every 100 milliseconds.
Every other device (all time stamp consumers) should have a receive PDO mapped for the highresolution
time stamp message. The message ID of each receive PDO used to receive a time
stamp should match the ID of the transmit PDO used to send the time stamp.
Configuring the devices in this fashion causes the time stamp producer to generate a transmit
PDO for every N sync messages. This PDO is received by each of the time stamp consumers on
the network and causes them to update their internal system times based on the message
content. The result is that all devices on the network act as though they share the same clock
input, and remain tightly synchronized.
Emergency Messages
A device sends an 8-byte emergency message (EMCY) when an error occurs in the device. It
contains information about the error type, and Copley-specific information. A device need only
send one EMCY message per event. Any device can be configured to accept EMCY messages.
42 Copley Controls