ELM327P datasheet(53/76 Pages) ELM

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ELM327DSH

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ELM327

always send eight bytes of data, and fill in unused byte

positions with FFs.

With the headers off, the multiline response looks

very similar to the multiline responses for ISO15765-4.

The first line shows the total number of bytes in the

message, and the other lines show the segment

number, then a colon, and the data bytes following.

Note that the byte count is a hexadecimal value (ie the

‘012’ shown means that there are 18 bytes of data).

The one line that shows the total number of data

bytes is actually called a ‘Connection Management’ or

‘TP.CM’ message. It has a specific format, but the only

bytes that are typically relevant are those that provide

the total message size in bytes. In order to see the

other bytes, you must turn CAN Auto Formatting off

(AT CAF0), and then repeat the request. Note that this

will only show the entire TP.CM message if you have

an ELM327 v1.4b, and not a previous version.

This has been a brief description of how to use

the ELM327 in a typical J1939 environment. If you can

monitor for information, make global requests as well

as specific ones, and receive single or multiframe

responses, then you have the tools necessary to at

least diagnose most vehicle problems.

Using J1939 (continued)

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.

order

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

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 (the latest update was September 2010). For

more information, visit the web sites:

FMS Standard

http://www.fms-standard.com

Bus FMS Standard

http://bus-fms-standard.com

ELM327P Datasheet(PDF) 53 Page - ELM Electronics

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