ELM624
Communicating with the ELM624
The ELM624 relies on a standard RS232 type
serial connection to communicate with the user. All
commands are sent to, and responses are received
from the ELM624 over this interface. The RS232 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).
ELM624 is not case-sensitive (so ‘ATZ’ is equivalent to
‘atz’, as is ‘AtZ’).
Understood and executed ‘AT’ commands are
signalled by the transmission of the two characters
‘OK’, while any misunderstood commands (syntax
errors) are signalled by a single question mark (‘?’)
being sent. When Control L commands are executed,
correct completion is signalled by the ELM624
transmitting the four status bytes received from the
LANC bus (sent as eight hexadecimal digits). To
reduce RS232 traffic, all responses are terminated
with a single carriage return character, and no line
feed character. Some users may wish to have their
software insert these linefeed characters to improve
readability.
There is a possibility that incomplete data strings
could be sent to the ELM624 for one reason or
another. To avoid problems in these cases, the
ELM624 will automatically time out and abort any
incomplete command after about 20 seconds. It will
then print a single question mark, and wait for the next
command to be sent.
Properly connected and powered, the ELM624 will
initially display the message:
ELM624 v1.0 (c)1999
In addition to identifying the version of the IC,
receipt of this string is a convenient way for users to
be sure that their connections are correct. After
displaying this message, the integrated circuit will be
ready for a command on the RS232 port, and will wait
indefinitely until a valid one is received.
Commands can either be for internally configuring
the ELM624, or for passing on to the LANC port. The
internal commands are distinguished by always
beginning with the characters ‘AT’, while the two
Control L bytes are simply a series of four hex digits.
See the following sections for further details.
One last note involves the internal priorities
assigned to the two busses. In all cases, the RS232
bus takes priority over the LANC bus, and will cause
any LANC transmissions to abort if activity is detected
on the RS232 bus.
Some other characteristics to note concerning the
commands are that extra characters are not permitted
(spaces, tabs, etc.), all commands must be terminated
with a carriage return character (hex ‘0D’), and the
AT Commands
The ELM624 can accept internal configuration
commands at any time, in much the same manner that
modems do. Any command sent to the ELM624 that
begins with the characters A followed by T is
considered an internal configuration or ‘AT’ command.
These are executed upon receipt of the terminating
carriage return character, and acceptance of a
command is acknowledged by the printing of the
characters ‘OK’.
The factory default settings should be sufficient for
most applications, and communications on the LANC
port can generally begin without requiring the issuance
of any AT commands, but some users may wish to
customize settings, such as turning the character echo
off, etc.
ATC0 and ATC1
These commands specify when the Control L status
bytes are to be returned on the RS232 bus. With
the C1 command, values are only sent when there
is a change from the previous four, while with C0
they are always sent. For most devices, setting C1
will have little noticeable effect, as the LANC
responses usually alternate between status and
time-code values, thus continually change. The
default is C1.
ATD0 and ATD1
These commands determine whether the first two
Control L words (0 and 1) are to be duplicated in
the next two words (2 and 3). If D0 is selected,
duplication will not occur, and words 2 and 3 will be
sent as ‘zeros’, while setting D1 will force the words
to be duplicated. The default is D1.
The following summarizes the ‘AT’ commands that
are recognized by the ELM624. Note that the
character ‘0’ is the number ‘zero’:
ELM624DSB
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