ELM624
ATE0 and ATE1
These commands control whether characters
received on the RS232 port are retransmitted (or
echoed) back to the host computer. To reduce
traffic on the RS232 bus, users may wish to turn
echoing off by issuing E0. Default is E1, echo on.
ATRn where ‘n’ is a Hex Digit
This sets the LANC command repeat value.
Although commands are only sent from the
computer to the ELM624 once, they are sent on the
Control L bus multiple times. While the Control L
standard requires that commands must be repeated
at least four successive times to be valid, the ATR
command allows this parameter to be modified for
experimentation or non-standard applications. The
default value is five (R5), and commands are
always sent at least once (R0 is treated as R1).
ATI
This causes the IC to identify itself. It simply sends
the power-on string (for a version 1.0 IC, it is
‘ELM624 v1.0 (c)1999’) and returns to the
command mode.
ATZ
This combination causes the chip to perform a
complete reset as if power were cycled off and then
on again. All settings are returned to their default
values.
Data Transfer - The LANC Protocol
Any valid four digit hex code that is received on
the RS232 port will be converted to Control L format
and transmitted out the LANC pin. The ELM624 makes
no effort to determine whether the codes are valid or
not. After sending the command, all responses
received on the port are reported back to the RS232
port using standard ASCII characters for the eight
hexadecimal digits that represent the 4 bytes received.
Note that control characters are not sent - the
hexadecimal digit ‘A’ is transmitted as decimal value
65, not 10.
All transfers on the LANC bus occur at a rate
determined by the device being controlled. The
camcorder, or other device provides all of the timing or
synchronizing pulses for the data transfer, and the
ELM624 (in this case) must sense these sync pulses
in order to send or receive data. If the controlled
device is not providing these pulses for any reason, a
‘NO SYNC’ error will result - check your cables and
power supplies.
A Control L ‘data frame’ consists of 8 sequential
bytes. Commands to the device (from the ELM624)
are sent during the first half of the frame, while the
second half (last four bytes) are for feedback from the
controlled device. Often, four bytes are not enough to
send all of the information, so data is multiplexed over
several frames. An example of this is the time codes
which contain information on days, hours, minutes and
seconds which require several bytes to represent.
The ELM624 does not send a command on the
LANC bus until it has received four valid hex digits and
ELM624DSB
a carriage return. The digits are combined in pairs to
form the first two words to be sent on the Control L bus
and, depending on the ATD option, may also be
duplicated and sent on the interface as bytes 3 and 4.
In the Control L standard, the first byte sent
usually signifies the type of device being spoken to
(eg. 1 for VTR and 2 for camera), as well as an
identifying device number. These correspond to the
first and second hex digits sent to the ELM624,
respectively. The second byte (digits 3 and 4) is the
actual command being sent. For example, the four
character command string:
1034
would normally be interpreted as ‘VTR #0 Play’, as the
code for play is 34. Similarly, 1030 would stop the
same VTR. Typical control codes follow:
30 Stop
36 Rewind
32 Pause
38 Fast Forward
34 Play
3A Record
8C Counter Reset
The Control L device will respond with a sequence
of 4 bytes (8 hex digits). The first byte (two digits) is
always a status byte, having typical values as follows:
02 Stopped
03 Fast Forwarding
04 Recording
06 Playing
72 Stopped - at tape beginning
83 Rewinding
The next nibble (third digit) is used to identify the
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Elm Electronics – Circuits for the Hobbyist
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