ELM327P datasheet(47/76 Pages) ELM

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ELM327

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ELM327DSH

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Using CAN Extended Addresses

Some vehicles with CAN interfaces use a data

format that is slightly different from what we have

described so far. The data packets look very similar,

except that the first byte is used for the receiver’s (ie

target’s) address. The remaining seven bytes are used

as described previously.

We refer to this type of addressing as ‘CAN

Extended Addressing’, and provide support for it with

the AT CEA commands. Perhaps an example would

better describe how to use them.

Here is a portion of a data transfer that was taken

from a vehicle. For the moment, ignore the first data

bytes on each line and only look at the remaining data

bytes (that are outlined in grey):

7B0 04 02 10 81 00 00 00 00

7C0 F1 02 50 81 00 00 00 00

7B0 04 02 21 A2 00 00 00 00

7C0 F1 10 16 61 A2 01 02 05

7B0 04 30 FF 00 00 00 00 00

7C0 F1 20 DF 01 00 04 09 01

7C0 F1 21 02 05 DF 01 00 04

7C0 F1 22 09 01 00 04 01 00

If you are familiar with the ISO 15765 data format,

you will be able to recognize that the data bytes shown

inside the box seem to conform to the standard. The

rows that begin with 02 are Single Frames, the one

that starts with 10 is a First Frame, while the one with

30 is a Flow Control, and the others are Consecutive

Frames.

The remaining bytes, shown outside the box, are

the standard 11 bit CAN ID, and an extra address

byte. The lines with F1 for the extra address are

directed to the scan tool (all scan tools generally use

F1 as the default address), and the other lines are

being sent to the vehicle’s module (at address 04).

Version 1.4 of the ELM327 is able to handle these

types of messages, but does require some setup. For

example, if the messages use 11 bit IDs with

ISO 15765 formatting, and the baud rate is 50 kbps,

then the PB command to configure protocol B is:

>AT PB 81 0A

Next, we’ll want to receive all messages with an ID

of 7C0, and send with an ID (header) of 7B0:

>AT CRA 7C0

>AT SH 7B0

Notice that there was a flow control message that

was sent in this group, but it’s not quite the same as

the one for OBD systems. For this reason, you’ll need

to define your own flow control with the following three

statements (we won’t show the OK’s any more, to

save space):

>AT FC SH 7B0

>AT FC SD 04 30 FF 00

>AT FC SM1

The final setup statement that you will need is to

tell the ELM327 to send to CAN Extended Address 04:

>AT CEA 04

Now everything is configured. Next, tell the IC to

use this protocol, and to bypass any initiation (as it is

not standard OBD, and would likely fail):

>AT SP B

>AT BI

That’s all. To exactly reproduce the flow of data

shown, you only need to send the relevant data bytes

and the ELM327 will add the rest:

>10 81

50 81

>21 A2

016

0: 61 A2 01 02 05

0: DF 01 00 04 09 01

1: 02 05 DF 01 00 04

2: 09 01 00 04 01 00

Notice that for some reason, this vehicle has sent

two segment 0’s, but that just means that it doesn’t

exactly follow the ISO 15765 protocol. The above

shows what the responses would look like with

formatting on, and headers off. If you change either,

the data exchange would look more like what we

initially showed.

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