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ELM329DSC
Elm Electronics – Circuits for the Hobbyist
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ELM329
Several European heavy duty truck and bus
manufacturers have joined to form an organization for
standardizing the way in which information is retrieved
from these large vehicles. The result of their work is
the FMS (or Fleet Management Systems) Standard,
and the Bus-FMS Standard.
The FMS standard is based on a subset of the
250 kbps J1939 protocol, which uses only broadcast
messages for the information. In order to not
compromise the integrity of the vehicle’s CAN bus, the
standard also specifies a gateway device to provide
separation between (potentially unskilled) users and
the critical control information on the vehicle.
The information contained in the FMS messages
is defined by PGNs, using the same PGN numbers as
for J1939. The difference is that they only define a
small subset of those specified by J1939.
To monitor the information provided by an FMS
gateway, simply use the AT MP command with the
The FMS Standard
We are occasionally asked about support for the
NMEA 2000 marine standard. Elm Electronics does
not provide specific support for this protocol, but our
ELM329 integrated circuit is very capable of working
with the protocol.
While the physical connectors may look quite a bit
different than those used for J1939, the CAN interface
and the data format is almost identical to that of the
J1939 standard. NMEA 2000 uses a 250 kbps data
rate, so the easiest way to get started is to select the
ELM329’s predefined protocol A. This is done with the
set protocol to A command:
>AT SP A
When you are finished and want to use the
ELM329 for standard OBDII protocols, don’t forget to
send the AT SP 0 command to reset it.
Many of the PGNs used for NMEA 2000 have
values that are greater than 65535, so the DP bit is
usually set. To monitor for most PGNs then, you can
not use the short version of the MP command. For
example, to monitor for the Engine Parameters PGN
(127488 or hex 1F200), you can not use:
>AT MP 1F200
The NMEA 2000 Standard
appropriate PGN number. We should caution that
some information (VIN, software version, etc.) is only
transmitted every 10 seconds, so some patience is
required when waiting for the data.
The FMS standard is completely open, and still
evolving (as of this writing, the latest update was
version 2.00, dated November 11, 2010). For more
information, visit the web sites:
as the ELM329 actually interprets that as a request for
PGN 1F20, and get 0 replies. To monitor for PGN
1F200, you must send:
>AT MP 01F200
If you keep the above in mind, the ELM329 will
prove to be a handy tool to use while experimenting
with NMEA 2000. It does have a couple of limitations
that must be kept in mind, though. As mentioned with
J1939, it is not capable of address negotiation. Also,
the ELM329 does not currently support the Fast
Packet protocol, which may be an issue for some
users.
For more information on the NMEA 2000 standard,