ELM325 Datasheet, PDF (6/31 Pages) ELM Electronics – J1708 Interpreter

ELM325
Communicating with the ELM325 (continued)
question mark. These include incomplete messages,
incorrect AT commands, or invalid hexadecimal digit
strings, but are not an indication of whether or not the
message was understood by the vehicle. One must
keep in mind that the ELM325 is a protocol interpreter
that makes no attempt to assess the content of
messages for validity – it only ensures that
hexadecimal digits were received, combined into
bytes, then sent out the J1708 port, and it does not
know if a message sent to the vehicle was appropriate
or not.
While processing J1708 messages, the ELM325
will continually monitor for an RS232 character
received. If it sees one, this will interrupt the IC, quickly
returning control to the user. Since the time to respond
varies with what the ELM325 was doing at the time,
software should always wait for the prompt character
(‘>’ or hex 3E) to be received, before beginning to
send the next command.
Finally, it should be noted that the ELM325 is not
case-sensitive, so the commands ‘ATZ’, ‘atz’, and
‘AtZ’ are all exactly the same to the ELM325. All
commands may be entered as you prefer, as no one
method is faster or better. The ELM325 also ignores
space characters and all control characters (tab, etc.),
so they can be inserted anywhere in the input to
improve readability.
One other feature of the ELM325 is the ability to
repeat the last command when only a single carriage
return character is received. This may be convenient if
you have sent a command and wish to repeat it in
order to obtain updates. If you simply send a carriage
return, then you do not have to resend the entire
command. The memory buffer only remembers one
previous command though – there is no provision in
the current ELM325 to provide storage for more.
ELM325DSA
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