ELM624
Overview
The following describes how to use the ELM624 to
there are also sections on how to use some of the
other features of this product as well.
For experimenting, all that is required is a PC or a
PDA with a terminal program (such as HyperTerminal
or ZTerm), and knowledge of one or two LANC
commands, which we provide in the following…
control, and to obtain information from your LANC
device. We begin by discussing just how to talk to the
IC, then how to adjust some options through the use of
‘AT’ commands, and finally go on to actually talk to the
LANC device, both obtaining status codes and sending
commands. For the more advanced experimenters,
Communicating with the ELM624
The ELM624 relies on a standard RS232 type
serial connection to communicate with the user. The
data rate is fixed at 9600 baud, with 8 data bits, no
parity bit, 1 stop bit, and no handshaking (often
referred to as 9600 8N1). All responses from the IC
will be terminated with a single carriage return
character and by default, a line feed character as well.
Make sure that your software is configured for this type
of communication.
carriage return appears. In this case, an internal timer
will automatically abort the incomplete message after
about 20 seconds, and the ELM624 will print a single
question mark to show that the input was not
understood (and was ignored).
Messages that are not understood by the ELM624
(syntax errors) will always be signalled by a single
question mark (‘?’). These include incomplete
messages, invalid hexadecimal digit strings, or
incorrect AT commands. It is not an indication of
whether or not the message was understood by the
LANC device. (The ELM624 is a protocol interpreter
that makes no attempt to assess LANC messages for
validity – it only ensures that either four or eight hex
digits were received, combined into bytes, and sent
out the LANC port. It cannot make judgement on the
actual bytes that were sent.)
Incomplete or misunderstood messages can also
occur if the controlling computer attempts to write to
the ELM624 before it is ready to accept the next
command (as there are no handshaking signals to
control the data flow). To avoid a data overrun, users
should always wait for the prompt character (‘>’)
before issuing the next command.
Finally, a few convenience items to note. The
ELM624 is not case-sensitive, so ‘ATZ’ is equivalent to
‘atz’, and to ‘AtZ’. Also, the device ignores space
characters as well as control characters (tab, linefeed,
etc.) in the input, so they can be inserted anywhere in
order to improve readability.
Properly connected and powered, the ELM624 will
initially display the message:
ELM624 v3.0
>
In addition to identifying the version of the IC,
receipt of this string is a convenient way to be sure
that the computer connections and the settings are
correct. However, at this point no communications
have taken place with the LANC device, so the state of
that connection is still unknown.
The ‘>’ character displayed above is the ELM624’s
prompt character. It indicates that the device is in its
idle state, ready to receive characters on the RS232
port. Characters sent from the computer can either be
intended for the ELM624’s internal use, or for
reformatting and passing on to the LANC device.
Commands for the ELM624 are distinguished from
those to the LANC device by always beginning with
the characters ‘AT’ (as is common with modems),
while commands for the LANC bus must contain only
the ASCII characters for hexadecimal digits (0 to 9 and
A to F). This allows the ELM624 to quickly determine
where the received characters are to be directed.
Whether an ‘AT’ type internal command or a hex
string for the LANC bus, all messages to the ELM624
must be terminated with a carriage return character
(hex ‘0D’) before it will be acted upon. The one
exception is when an incomplete string is sent and no
ELM624DSD
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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