WIKA D-21-9 - Manual (Page 42)

D-20-9 / D-21-9 GB
WIKA Additional Instructions Pressure Transmitter with CANopen Interface D-20-9 / D-21-9 42
Error Control Services
Through Error control services the NMT detects failures in a CAN-based Network. Local errors in a node lead
to a change of state (PREOPERATIONAL). Error Control services are achieved principally through periodically
transmitting of messages by a device. There exist two possibilities to perform Error Control.
The guarding is achieved through transmitting guarding requests (Node guarding protocol) by the NMT
Master. If a NMT Slave has not responded within a defined span of time (node life time) or if the NMT Slave’s
communication status has changed, the NMT Master informs its NMT Master Application about that event. If
Life guarding (NMT slave guarded NMT master) is supported, the slave uses the guard time and lifetime factor
from its Object Dictionary to determine the node life time. If the NMT Slave is not guarded within its life time,
the NMT Slave informs its local Application about that event. If guard time and life time factor are 0 (default
values), the NMT Slave does not guard the NMT Master. Guarding starts for the slave when the first remote-
transmit-request for its guarding identifier is received. This may be during the boot-up phase or later.
The heartbeat mechanism for a device is established through cyclically transmitting a message by a heartbeat
producer. One or more devices in the network are aware of this heartbeat message. If the heartbeat cycle fails
for the heartbeat producer the local application on the heartbeat consumer will be informed about that event.
Heartbeat Protocol
The Heartbeat Protocol defines an Error Control Service without need for remote frames. A Heartbeat
Producer transmits a Heartbeat message cyclically. One or more Heartbeat Consumer receive the indication.
The relationship between producer and consumer is configurable via the object dictionary. The Heartbeat
Consumer guards the reception of the Heartbeat within the Heartbeat Consumer Time. If the Heartbeat is not
received within the Heartbeat Consumer Time a Heartbeat Event will be generated.
r: reserved (always 0)
s: the state of the Heartbeat producer
0: BOOTUP
4: STOPPED
5: OPERATIONAL
127: PRE-OPERATIONAL
If the Heartbeat Producer Time is configured on a device the Heartbeat Protocol begins immediately. If a
device starts with a value for the Heartbeat Producer Time unequal to 0 the Heartbeat Protocol starts on the
state transition from INITIALISING to PRE-OPERATIONAL. In this case the Bootup Message is regarded as
first heartbeat message. It is not allowed for one device to use both error control mechanisms Guarding
Protocol and Heartbeat Protocol at the same time. If the heartbeat producer time is unequal 0 the heartbeat
protocol is used.