5 Allocation of Buffer Memories
5.8 [BFM #26] FROM/TO Watchdog
38
FX
3U
-J1939 User's Manual
*1.
If the arbitrary address capability is activated (BFM #25 bit 2 = ON) and the address set in BFM #27/
#28 is in the "dynamic" address range, the FX
3U
-J1939 will start to negotiate with other nodes in the
network for a node address. If an address conflict occurs, the FX
3U
-J1939 will attempt to claim a new
address and set BFM #29 bit 9 to ON.
If the module is set to single address capable (arbitrary address capability is de-activated), an address
conflict will cause the FX
3U
-J1939 to send a "can not claim" message and stop exchanging data with
the bus.
The status of this bit is stored to Flash ROM.
For details on the node address, refer to Section 5.9 and Section 5.10
For error status (BFM #29), refer to Section 12.2
*2.
There are two events that might cause the FX
3U
-J1939 to lose permission to use its current node
address:
-
The reception of a "commanded address" message
-
A node with higher priority claims the address currently used by the FX
3U
-J1939
In such a case, bit 3 is set to ON when a new a node address is claimed successfully by the FX
3U
-
J1939. If no new node address could be claimed, BFM #29 bit 1 is set to ON.
*3.
This bit must be set to ON to start data exchange with other network nodes. The configuration of the
module can only be changed while this bit is OFF.
*4.
While this flag is ON, the FX
3U
-J1939 is initializing.
5.8
[BFM #26] FROM/TO Watchdog
The FROM/TO Watchdog can be used to monitor if the PLC program cyclically accesses data BFMs #100 to
#399 or the extended data area in BFM #1300 to #1799.
After the first FROM/TO on the data BFM, the Watchdog will check if the next access to the data BFMs takes
place before the time set in BFM #26 expires.
BFM #26 sets the Watchdog timer in units of 10 ms [default value: K20 (200 ms)].
Note
• Any new valid value written to BFM #21, #24, #25 bit 2, #26 or #27 is automatically stored to flash ROM.
The maximum number of writes to the built-in flash ROM is 10,000 times.
Therefore, when creating a program, do not frequently write to such buffer memories.
• If the watchdog expires, bit 7 in BFM #29 is set to ON, and the "PLC RUN>STOP messages" defined in
BFM #1900 to #1927 are transmitted on the network.
• The FROM/TO watchdog can be restarted by writing the setting value to BFM #26 again, which will also
reset the error flag in BFM #29.
• If the watchdog function is not required, it can be deactivated by writing K0 to BFM #26.
Bit 4
OFF:
Request configuration mode
ON:
Request online mode
*3
Bit 5, 6
Not used
Not used
Bit 7
Module initialization state
*4
Bit 8 to 15
Not used
Note
If a configuration BFM was changed during online mode, BFM #29 bit 5 is set ON.
Note
• During this time, do not write (TO instruction, etc) to any BFMs.
If write access is performed, FX
3U
-J1939 will cause an error in BFM #29 bit 5.
• During this time, do not read (FROM instruction, etc) any BFMs other than BFM #25, as the current
values of the BFM might change during initialization.
Bit
Access
FROM (Read Access)
TO (Write Access)
