CAN
CX8050, CX8051 - Embedded-PCs for
CANopen and CAN
70
Version: 1.4
Guarding procedure
Protocol
The toggle bit (t) transmitted in the first guarding telegram has the value
0
. After this, the bit must change
(toggle) in every guarding telegram so that the loss of a telegram can be detected. The node uses the
remaining seven bits to transmit its network status (s):
s
Status
4 = 0x04
Stopped (formerly: prepared)
5 = 0x05
Operational
127 = 0x7F
Pre-Operational
Example
The guarding message for node 27 (0x1B) must be requested by a remote frame having identifier 0x71B
(1819
dec
). If the node is
Operational
, the first data byte of the answer message alternates between 0x05 and
0x85, whereas in the
Pre-Operational
state it alternates between 0x7F and 0xFF.
Guard time and life time factor
If the master requests the guard messages in a strict cycle, the slave can detect the failure of the master. In
this case, if the slave fails to receive a message request from the master within the set
Node Life Time
(a
guarding error), it assumes that the master has failed (the watchdog function). It then puts its outputs into the
error state, sends an emergency telegram, and returns to the pre-operational state. After a guarding time-out
the procedure can be re-started by transmitting a guarding telegram again.
The node life time is calculated from the guard time (object 0x100C) and life time factor (object 0x100D)
parameters:
Life time = guard time x life time factor
If either of these two parameters is "0" (the default setting), the master will not be monitored (no life
guarding).
Summary of Contents for CX8050
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