ELM624
Talking to Your LANC Device
The ELM624 allows for two types of messages.
When you send a string of characters to the ELM624
that begins with the letters ‘A’ and ‘T’, the message is
used internally as discussed before. If the message is
a series of hexadecimal digits, it will be assumed that
you are trying to talk to the LANC device.
Hexadecimal digits can take on values from 0 to 9,
and from A to F, representing decimal values 0 to 15.
Two hex digits are combined to form a byte, and are
usually shown that way (in pairs). It is very common for
charts of Control L/LANC codes to use hex digits to
show the control commands, so for that reason, the
ELM624 was designed to use them as well.
When the ELM624 receives hexadecimal digits, it
will also check to be sure that you have provided either
four or eight of them. If there were four hex characters
received, they will be combined in pairs to form the
first two control bytes, and the two remaining control
bytes will be set depending on the AT D0/1 setting. If
there were eight hex digits received, they will be
combined into four pairs and used for the four
command bytes. Once the ELM624 has the
commands ready, it will synchronize to the LANC
device, and send them. Note that the use of four
control bytes (eight hex digits) is quite rare but is a
feature provided by the ELM624 in case you wish to
experiment. For most devices, only the two command
bytes (four hex digits) are needed, and that is what we
show here.
After sending a command, all responses received
from the LANC device are reported back to the user,
just as if an AT MA command had been issued. If the
default formatted data option is selected, all data will
be shown as hex digits, using standard ASCII
characters. Control characters are never sent – the
hexadecimal digit ‘A’ for example, is transmitted as the
decimal value 65 (a letter ‘A’), and not as 10 (a
linefeed character).
nibble is often the type of device (eg. 1 for VTR, or 2
for camera), and the second nibble is a unique
identifier for that device (ie. the device number). Often
this second digit is shown as an ‘8’, but it does not
need to be. These two digits correspond to the first
and second hex digits that need to be sent to the
ELM624.
The second command byte (the third and fourth
hex digits) is the actual command for the device being
controlled. Some typical control codes are:
30 Stop
32 Pause
34 Play
2C Eject
36 Rewind
38 Fast Forward
3A Record
8C Counter Reset
It is not the purpose of this data sheet to show all
possible command codes, as they vary by device and
manufacturer. The above ones seem to be very
common however, and should get you started.
As our first example, assume that the camcorder
is on, and selected for play (VTR) mode. The first thing
we might want to do is be sure that it is ready to
accept commands. At the prompt, ask the ELM624 to
check the sync:
>AT CS
SYNC OK
If all is well, you should get the OK message as
shown above. If we wish to play the tape, we might
now enter the four digit command:
>1034
This command can better be understood if we
separate the first few characters, and read them as
follows:
1
0
3 4
VTR
#0
Play
In order to send a command to the LANC device
then, all the user need do is type four hex digits then
press return, and all of the data conversion, formatting,
synchronizing, etc. is done by the ELM624.
There are several sources of information on the
web for command codes, and the manufacturer of your
camcorder may be able to provide some information
as well. For the purpose of this discussion, we will look
at some of the more generic codes that might typically
be found.
The command is ‘VTR #0 Play’ (as the code for
play is 34). The above talks to device #0, but much of
the literature often shows commands being sent to #8.
No problem with the ELM624 - for this example, you
would simply use 1834 instead of 1034.
Similarly, 2130 could be sent to the ELM624, to
mean ‘Camera #1 Stop’. Again, note that there does
not seem to be a completely standard set of
commands, so you will have to check with your
manufacturer to be sure of which ones are supported
by your device.
In the Control L standard, the first byte sent
usually identifies the device being spoken to. The first
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