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data bytes that are received in the frame will be
removed, and any messages with invalid PCI bytes will
be ignored. (When monitoring, however, messages
with invalid PCI bytes will be shown, with a ‘<DATA
ERROR’ message beside them).
Multi-frame responses may be returned by the
vehicle with ISO 15765 and J1939. To make these
more readable, the Auto Formatting mode will extract
the total data length and print it on one line, then show
each line of data with the segment number followed by
a colon (‘:’), and then the data bytes.
You may also see the characters 'FC:' on a line (if
you are experimenting). This identifies a Flow Control
message that has been sent as part of the multi-line
message signalling. Flow Control messages are
automatically generated by the ELM329 in response to
a ‘First Frame’ reply, as long as the CFC setting is on
(it does not matter if auto formatting is on or not).
Another type of message – the RTR (or ‘Remote
Transmission Request’) – will be automatically hidden
for you when in the CAF1 mode, since they contain no
data. When auto formatting is off (CAF0), you will see
the characters 'RTR' printed when one of these frames
has been received.
Turning the CAN Automatic Formatting off (CAF0),
will cause the ELM329 to print all of the received data
bytes. No bytes will be hidden from you, and none will
be inserted for you. Similarly, when sending a data
request with formatting off, you must provide all of the
required data bytes exactly as they are to be sent –
the ELM329 will not perform any formatting for you
other than to add some trailing 'padding' bytes to
ensure that eight data bytes are sent, if required. This
allows operation in systems that do not use PCI bytes.
Note that turning the display of headers on (with
AT H1) will override some of the CAF1 formatting of
the received data frames, so that the received bytes
will appear much like in the CAF0 mode (ie. as
received). It is only the printing of the received data
that will be affected when both CAF1 and H1 modes
are enabled, though; when sending data, the PCI byte
will still be created for you and padding bytes will still
be added. Auto Formatting on (CAF1) is the default
setting for the ELM329.
CEA [ turn off the CAN Extended Address ]
The CEA command is used to turn off the special
features that are set with the CEA hh command.
CEA hh [ set the CAN Extended Address to hh ]
Some CAN protocols extend the addressing fields
by using the first of the eight data bytes as a target or
receiver’s address. This type of formatting does not
comply with any OBD standard, but by adding it, we
allow for some experimentation.
Sending the CEA hh command causes the
ELM329 to insert the hh value as the first data byte of
all CAN messages that you send. It also adds one
more filtering step to received messages, only passing
ones that have the Tester Address in the first data byte
position (in addition to requiring that ID bits match the
patterns set by AT CF and CM, or CRA). The AT CEA
hh command can be sent at any time, and changes
are effective immediately, allowing for changes of the
address ‘on-the-fly’. There is a more lengthy
discussion of this extended addressing in the ‘Using
CAN Extended Addresses’ section on page 57.
The CEA mode of operation is off by default, and
once on, can be turned off at any time by sending AT
CEA, with no address. Note that the CEA setting has
no effect when J1939 formatting is on.
CF hhh [ set the CAN ID Filter to hhh ]
The CAN Filter works in conjunction with the CAN
Mask to determine what information is to be accepted
by the receiver. As each message is received, the
incoming CAN ID bits are compared to the CAN Filter
bits (when the mask bit is a ‘1’). If all of the relevant
bits match, the message will be accepted, and
processed by the ELM329, otherwise it will be
discarded. This version of the CAN Filter command is
used to set filters with 11 bit ID CAN systems. Only the
rightmost 11 bits of the provided nibbles are used, and
the most significant bit is ignored.
CF hh hh hh hh [ set the CAN ID Filter to hhhhhhhh ]
This command allows all four bytes (actually 29
bits) of a CAN Filter to be set at once. The 3 most
significant bits will always be ignored, and may be
given any value. This command may be used to create
11 bit ID filters as well, since they are stored in the
same locations internally (entering AT CF 00 00 0h hh
is exactly the same as entering the shorter AT CF hhh
command).
CFC0 and CFC1 [ CAN Flow Control off or on ]
The ISO 15765-4 CAN protocol expects a ‘Flow
AT Command Descriptions (continued)
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