Siemens SIMATIC PN/J1939 LINK Operating Instructions Manual page 20

Functions
4.1 J1939 protocol
Transport protocols
Parameter groups with a maximum data length of 8 bytes can be transmitted within a J1939
data packet.
The following transport protocols are available for the transmission of data volumes larger
than 8 bytes.
● BAM (Broadcast Announce Message)
● CMDT (Connection Mode Data Transfer)
BAM messages are sent to all J1939 devices and require no handshaking.
CMDT messages are exchanged peer-to-peer between two J1939 devices. CMDT works
with a handshake method for data flow control.
DM messages
J1939 ECUs send DM messages to report their active DTCs (Diagnostic Trouble Codes) and
the corresponding lamp status. PN/J1939 LINK can read diagnostic data from the other
connected ECUs. The structure of a DM message corresponds to that of a standard PGN.
Transmission takes place via a multipackage protocol (BAM).
DM1 messages have a PGN (Parameter Group Number) of 65226 and a cycle of 1 second.
If data lengths of up to 512 bytes are sufficient, standard input modules can be used for the
configuration.
For data lengths greater than 512 bytes, configuration takes place via input proxy modules.
The maximum data length is 1785 bytes.
If the PGN 65226 is configured in TIA as an input module with a data length of greater than 8
bytes, a corresponding diagnostics alarm is sent to the S7 controller if there is a change of
the received DM1 data compared to the previous value.
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SIMATIC PN/J1939 LINK
Operating Instructions, 12/2018, A5E45307564-AA