7 Layer 2 Communication Mode (11/29 bit ID)
7.2 [BFM #1100 to #1267] Pre-defined Layer 2 Messages Parameter
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FX
3U
-J1939 User's Manual
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Introduc
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Specifi
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Inst
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Al
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J1939 C
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La
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C
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Proc
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7.2.2
Pre-defined Layer 2 receive messages
This subsection describes parameters A to D for the receive message.
1. Parameter A and B for each Layer 2 message
Set the source CAN ID of the received message to parameter A and B. CAN-ID is as follows, corresponding
to the function mode to be used.
Set parameter A and B of unused Layer 2 messages to HFFFF.
For function mode, refer to Section 5.4
2. Parameter C and D for each Layer 2 message
Set the filter for the ID set in parameter A and B. If the filter is set to H00000000, incoming messages are
checked for an exact match with the ID set in parameter A and B. Any bit set in the filter will be omitted when
comparing received IDs with the ID set in parameter A and B.
Example 1:
Layer 2 message 1 parameter A/B = H00000181
Layer 2 message 1 parameter C = H00000000
BFM #100 to #106 store received messages with the CAN-ID H181 only. Relation between received CAN
message, BFM #20 bit 0 and "RTR/new/DLC" high byte is shown below.
The flags "RTR/new/DLC" are cleared by PLC program after . They remain H00 after , because there
was no message stored between and . The first received CAN message that matches parameter A/B
and C/D is stored into the internal buffers, and as this is the only message between and , the high byte
value is set to H03. The high byte value H07 after shows that the buffer was overwritten at least once (in
this sample two times) since . The data bytes in the BFM are the data received with the last message.
Note
In this sample it is expected that the PLC program resets the status/command flags after reading the data at
, ,
and .
Parameter
Description
Default Value
Layer 2 message number parameter A Reception CAN-ID low word
HFFFF
Layer 2 message number parameter B Reception CAN-ID high word
HFFFF
Layer 2 message number parameter C Reception ID filter bit mask low word
H0000
Layer 2 message number parameter D Reception ID filter bit mask high word
H0000
Function Mode
Description
layer 2 communication
(11 bit ID) mode
Store CAN-ID in the lower 11 bits (bit 0 to 10) of parameters A and B by 32 bit instructions.
layer 2 communication
(29 Bit ID) mode
Store CAN-ID in the lower 29 bits (bit 0 to 28) of parameters A and B by 32 bit instructions.
CAN bus
BFM #20
bit 0
RTR/new/DLC
high byte
Message
H0181
Message
H0181
Message
H0181
Message
H0181
H03 (new frame + data
between and )
H00
Hxx
H00 (no new data
between and )
H07 (new frame + data
and overflow between
and )
