ELM329
Multiline Responses (continued)
multiline responses.
Looking at the first digits of these responses, you
can see that some begin with 7E8, and some begin
with 7E9, which are the CAN IDs representing ECU#1
and ECU#2, respectively. Grouping the responses by
ECU gives:
7E8 10 13 49 04 01 35 36 30
7E8 21 32 38 39 34 39 41 43
7E8 22 00 00 00 00 00 00 31
and
7E9 10 13 49 04 01 35 36 30
7E9 21 32 38 39 35 34 41 43
7E9 22 00 00 00 00 00 00 00
From these, the messages can be assembled in
their proper order. To do this, look at the byte following
the CAN ID - it is what is known as the PCI byte, and
is used to tell what type of data follows. In this case,
the PCI byte begins with either a 1 (for a ‘First Frame’
message), or a 2 (for the ‘Consecutive Frames’). The
second half of the PCI byte shows the order in which
the information is to be assembled (ie. the segment
number). In this case, the segment numbers are
already in order, but if they had not been, it would
have been necessary to rearrange the messages to
place them in order. The actual data can then be
extracted from the remaining bytes in each line.
The information presented here was only meant to
provide an overview of how long messages are
handled by the ISO 15765 standard. If you do wish to
learn more about the actual mechanism, we urge you
to purchase a copy of the standard, and study it.
ELM329DSB
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