ELM329LP datasheet(39/87 Pages) ELM

39 / 87 page

39 of 87

ELM329L

ELM329L DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Multiline Responses

There are occasions when a vehicle must respond

with more information than is able to fit in a single

‘message’. In these cases, it responds with several

data frames which the receiver must assemble into

one complete response. The following shows how this

is done with the ISO 15765-4 protocol.

Consider a request for the vehicle identification

number, or VIN. This is available from newer vehicles

using a mode 09, PID 02 request (but was not initially

an OBD requirement, so may not be supported by your

vehicle). Here is a typical response that the ELM329

might show:

>0902

014

0: 49 02 01 31 44 34

1: 47 50 30 30 52 35 35

2: 42 31 32 33 34 35 36

The CAN Formatting has been left on (the default),

making the reading of the data easier. With formatting

on, the lines begin with a sequence number and then a

colon (‘:’) to separate it from the data bytes. CAN

systems add this single hex digit (it goes from 0 to F

then repeats), to provide an aid for reassembling the

data.

The first line of this response says that there are

014 bytes of information in total. That is 14 in hex, or

20 in decimal, which agrees with the 6 + 7 + 7 bytes

shown on the three lines. The VIN numbers are

generally 17 digits long, however, so how do we

assemble the VIN from 20 digits?

Looking at the first three bytes of the response,

you can see that the first two are the familiar 49 02, as

this is a response to an 09 02 request. They can be

ignored. The third byte (the ‘01’), tells the number of

data items that are to follow (the vehicle can only have

one VIN), and it is not part of the VIN. Eliminating the

first three bytes then leaves 17 data bytes which may

be used to form the vehicle identification (serial)

number. To do this requires first assembling the 17

data bytes in order:

31 44 34 47 50 30 30 52 35 35 42 31

32 33 34 35 36

The above data values actually represent the

ASCII codes for all the characters of the VIN, so the

final step is to convert those codes into the actual

characters that they represent. ASCII tables are freely

available on the web, and may be used to yield the

following VIN for the vehicle:

1 D 4 G P 0 0 R 5 5 B 1 2 3 4 5 6

From this example, you can see that the format of

the data received may not always be obvious. For this

reason, a copy of the SAE J1979 (ISO 15031-5)

standard would be essential if you are planning to do a

lot of work with this, for example if you were writing

software to display the received data.

The next example shows how similar messages

might occasionally be ‘mixed up’ in a CAN system. We

ask the vehicle for Calibration ID #1 with an 09 04

request and receive the following response:

>09 04

013

0: 49 04 01 35 36 30

1: 32 38 39 34 39 41 43

013

0: 49 04 01 35 36 30

2: 00 00 00 00 00 00 31

1: 32 38 39 35 34 41 43

2: 00 00 00 00 00 00 00

which is quite confusing. The first group (the 013, 0:, 1:

group) seems to make some sense (but the number of

data bytes do not agree with the response), and the

remaining data is also very confusing, as it has two

segment twos. It seems that two ECUs are responding

and the information is getting mixed up. Which ECU do

the responses belong to? The only way to know is to

turn on the headers, and repeat your request. Turning

the headers on, is simply a matter of sending H1:

>AT H1

Then you can repeat the request:

>09 04

7E8 10 13 49 04 01 35 36 30

7E8 21 32 38 39 34 39 41 43

7E9 10 13 49 04 01 35 36 30

7E8 22 00 00 00 00 00 00 31

7E9 21 32 38 39 35 34 41 43

7E9 22 00 00 00 00 00 00 00

This time, the order appears to be the same, but

be aware that it may not be – that is why the standard

requires that sequence codes be transmitted with

ELM329LP датащи(PDF) 39 Page - ELM Electronics

ELM329LP датащи(HTML) 39 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

датащи скачать

ссылки URL