7 Layer 2 Communication Mode (11/29 bit ID)
7.2 [BFM #1100 to #1267] Pre-defined Layer 2 Messages Parameter
68
FX
3U
-J1939 User's Manual
Example 2:
Layer 2 message 2 parameter A = H00000180
Layer 2 message 1 parameter C = H00000006
BFM #107 to #113 stores received messages with CAN-IDs H180, H182, H184 and H186 because the ID bits
1 and 2 are not evaluated. Relation between received CAN message, BFM #20 bit 0 and "Status/Control
Flags" is shown below.
Note
• All four messages are stored in the same location. If more than one of the messages with ID H180, H182,
H184 or H186 is received between two write operations (BFM #20 bit 0 = ON), only the last received CAN-
ID, DLC, and data is available in BFM #107 to #113.
• In this sample, it is expected that the PLC program resets the status/command flags after reading the data
at , ,
and .
Behavior until is similar to that described in example 1.
Same as in the first example, the high byte value H07 after shows that the buffer was overwritten at least
once, since and the data bytes in the BFM are also the data received with the last message.
But this time, it is required to check the 11 bit CAN-ID in the corresponding Layer 2 message (BFM #100 to
#399) to determine which message ID was received. In this case the last message is H0180, and the data of
this message is stored to the data BFMs. The data of messages H0182 and H0186 are lost.
CAN bus
BFM #20
bit 0
RTR/new/DLC
high byte
Message
H0184
Message
H0182
Message
H0186
Message
H0180
H00
Hxx
H00 (no new data
between and )
H03 (new frame + data
between and )
H07 (new frame + data
and overflow between
and )
