ELM624
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Connection Diagram
PDIP and SOIC
(top view)
V
DD
V
SS
Control L to RS232 Interpreter
The Control L or LANC interface is an industry
standard introduced by the Sony Corporation for
controlling audio and video devices. It uses a bit
serial data format, and requires that the controller be
synchronized to the controlled device something
which is difficult to do using standard serial
interfaces. The ELM624 is an 8 pin integrated circuit
that transparently performs this function for you.
All user interaction with the ELM624 is by
standard ASCII characters over an RS232 interface.
There is no special formatting required, other than
perhaps an understanding of the hexadecimal
numbering system, nor is there a need for a powerful
PC - virtually any model with a serial port will do.
Since the ELM624 was designed to provide a
cost-effective way for people to experiment with the
Control L system, many features typically found in
commercial devices, such as RS232 handshaking,
variable baud rates, extra buffering of signals, etc.
have not been implemented. Responses are kept to
a minimum as well (eg. a single question mark is
returned for a misunderstood command), but the
general principles of operation are demonstrated
and for many applications, this is all that is required.
Low power CMOS design
Enable input allows control of multiple devices
Configurable with standard AT commands
ASCII output formatted as standard hex digits
Minimum of external components required
Most Control L formats supported
Internal pullup resistors simplify the interface
Crystal controlled for timing accuracy
Video editors
Time-lapse recording controllers
Programmed control of A/V equipment
Remote camera controls
LANC
Tx
Description
Applications
Block Diagram
1 of 11
Features
ELM624DSC
Enable
Rx
1
2
3
8
7
6
5
4
XT1
XT2
Tx
RS232
Interface
Control
5
Control L
Interface
3.58MHz
2
3
XT1
XT2
Enable
4
6
LANC
7
V
DD
V
SS
Rx
V
DD
ELM624
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Pin Descriptions
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface
mount type of package. To order, add the appropriate suffix to the part number:
300 mil Plastic DIP............................... ELM624P
200 mil SOIC..................................... ELM624SM
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Control L, LANC, and Sony are registered trademarks of the Sony Corporation.
All rights reserved. Copyright 1999 to 2002 by Elm Electronics.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
V
DD
(pin 1)
This pin is the positive supply pin, and should always
be the most positive point in the circuit. Internal
circuitry connected to this pin is used to provide
power on reset of the microprocessor, so an external
reset signal is not required. Refer to the Electrical
Characteristics section for further information.
XT1 (pin 2) and XT2 (pin 3)
A 3.579545MHz NTSC television colourburst crystal
is connected between these two pins. Crystal
loading capacitors (typically 27pF) will also normally
be connected between each of the pins and Vss.
Enable (pin 4)
This is an active high input which allows the ELM624
to accept or provide RS232 data. When at a high
level (or open-circuited), the ELM624 behaves as in
previous versions, continuously providing status
updates and responding to RS232 commands.
When this input is low, RS232 activity is ignored by
the IC, and no status updates are provided.
This pin was formerly used as an active low reset
input for v1.x ICs, but has now been discontinued.
Users which require the reset function can place a
special request for v1.1 ICs, which are functionally
the same as that described here except for the lack
of an enable pin.
Rx (pin5)
The computer's RS232 transmit signal is directly
connected to this pin through a single current limiting
resistor (typically about 47K
). Internal signal
inversion and Schmitt trigger waveshaping provide
the necessary signal conditioning.
Tx (pin 6)
This is the RS232 data output pin. The signal polarity
is compatible with most interface ICs, and the drive is
sufficient to allow interfacing using only a single PNP
transistor if desired. See the Example Applications
section for more details.
LANC (pin 7)
This is the open drain Control L (LANC) interface pin.
An internal pullup resistor is provided for a nominal
drain load.
V
SS
(pin 8)
Circuit common is connected to this pin. This is the
most negative point in the circuit.
ELM624DSC
Control L and LANC
The terms Control L and LANC mean the same thing, and are used interchangeably throughout the following.
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
ELM624
Electrical Characteristics
Absolute Maximum Ratings
Storage Temperature....................... -65C to +150C
Ambient Temperature with
Power Applied....................................-40C to +85C
Voltage on V
DD
with respect to V
SS
............ 0 to +7.5V
Voltage on any other pin with
respect to V
SS
........................... -0.6V to (V
DD
+ 0.6V)
Note:
Stresses beyond those listed here will likely damage
the device. These values are given as a design
guideline only. The ability to operate to these levels
is neither inferred nor recommended.
3 of 11
All values are for operation at 25C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below.
Characteristic
Minimum
Typical
Maximum
Conditions
Units
Supply Voltage, V
DD
4.5
5.0
5.5
V
V
DD
rate of rise
0.05
V/ms
Average Supply Current, I
DD
1.0
2.4
mA
Notes:
1. This integrated circuit is produced with a Microchip Technology Inc.'s PIC12C5XX as the core embedded
microcontroller. For further device specifications, and possibly clarification of those given, please refer to the
appropriate Microchip documentation.
2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved
using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as
may be obtained through direct connection to solar cells, or some charge pump circuits.
3. Device only. Does not include any load currents.
4. The value of the internal pullup resistance is both supply and temperature dependent.
5. This specification represents the current flowing through the protection diodes when applying large voltages
to the Rx input (pin 5) through a current limiting resistance. Currents quoted are the maximum continuous.
6. Nominal data transfer rate. Assumes that a 3.58 MHz crystal is used as a frequency reference. Data is
transferred to and from the ELM624 with 8 data bits, no parity, and 1 stop bit (8N1).
Input low voltage
V
SS
0.15 V
DD
V
Input high voltage
V
DD
V
0.85 V
DD
Output low voltage
0.6
V
Output high voltage
V
V
DD
- 0.7
Current (sink) = 8.7mA
Current (source) = 5.4mA
see note 2
ELM624DSC
Internal pullup resistances
(see note 4)
500
K
300
600
Pin 4 (Enable)
see note 3
Rx pin input current
mA
see note 5
-0.5
Pin 7 (LANC)
K
30
20
50
RS232 Baud Rate
baud
see note 6
9600
+0.5
Enable input setup time
sec
15
4 of 11
ELM624
ELM624DSC
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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
are terminated with a single carriage return character,
and optionally a line feed character as well. Make sure
your software is configured properly for the mode you
have chosen.
Properly connected and powered, the ELM624 will
initially display the message:
ELM624 v2.0
If you have elected to add linefeeds after line
ends, the cursor will now be blinking on the next line.
In addition to identifying the version of the IC, receipt
of the above string is a convenient way for users to be
sure that their connections are correct.
After displaying this initial message, the integrated
circuit will be ready to receive commands on the
RS232 lines. These commands consist of either 3 or 4
ASCII characters that are terminated with a single
carriage return character. Note that there is no prompt
character sent by the IC to indicate that it is in the
`receive mode'. (This is done in order to reduce the
number of bytes sent and thus maximize the
processing time between the bursts of data bytes.)
RS232 commands that are sent to the ELM624
can either be for internally configuring the IC, or for
passing on to the LANC device. The internal
commands are distinguished from the others by
always beginning with the two characters `AT', while
the Control L commands will always be a series of four
hexidecimal digits. This allows the ELM624 to quickly
determine where commands are to be directed. See
the following sections for further details.
In sending commands from a terminal program,
some users may wish to insert extra characters
(spaces or tabs) to improve the readability of their
input. This is permitted, as the ELM624 simply ignores
these characters. Also for convenience, the ELM624 is
not case-sensitive, so `ATZ' is equivalent to `atz', and
to `AtZ'. This allows you to type commands in what-
ever way you prefer.
All commands must be terminated with a carriage
return character (hex `0D') before they will be acted
upon. A word of caution, though if a linefeed
character is sent by the computer after the terminating
carriage return, it could be interpreted as the start of a
new command line unless the ELM624 is expecting it.
If you cannot turn the linefeeds off in your software, be
sure that the ELM624 is set consistently, with linefeed
generation turned on (see the ATL1 Command in the
next section).
There is a possibility that data strings sent by the
computer (or PDA) could be incomplete for one reason
or another, and no carriage return is ever received. To
avoid problems in these cases, the ELM624 will
automatically abort any incomplete command after
about 20 seconds. It will then print a single question
mark, and wait for another command to be sent.
There are two replies that can normally be
expected from the ELM624. Understood and executed
`AT' commands are acknowledged by the ELM624
sending the two characters `OK', while misunderstood
commands (syntax errors) are signalled by a single
question mark (`?'). When Control L commands are
executed, correct completion is signalled only by the
ELM624 transmitting the four status bytes (sent as
eight hexadecimal digits). There will be no `OK' sent in
this case.
One last note involves internal priorities. When the
Enable input is at a high level, activity on the RS232
bus will always interrupt activity on the LANC side. In
some cases it will be delayed, however, until the
ELM624 completes what it is doing. This is a change
from the v1.0 software where all activity was
immediately aborted with RS232 activity. If your
software had counted on an abort with activity, it will
have to be updated.
To expand on this, if there is activity on the RS232
Rx line while the IC is in the middle of transmitting a
response, it will always complete sending the line, and
will send the terminating carriage return before
returning to process the RS232 input. Similarly, if a
command is being sent to the Control L device when
an input occurs, the command will finish before the
ELM624 will accept the RS232 input. In this case, no
status reponse will be displayed. During the time that
the ELM624 is completing what it is doing, it will not
store RS232 characters it will only note that there
has been activity.
When controlling the ELM624 from your keyboard,
you cannot choose when to interrupt the ELM624, and
in fact it will make little difference. Under computer
control however, one should always look for a
terminating carriage return (and a linefeed character if
enabled) before beginning to send a command. This
will ensure that the ELM624 is in an idle period,
waiting for input, and is not in fact being interrupted.
5 of 11
ELM624
ELM624DSC
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
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 which
begins with the letter `A' followed by the letter `T' is
assumed to be an internal configuration (or `AT')
command. These commands are executed upon
receipt of the terminating carriage return character,
and acceptance of such a command is acknowledged
by the printing of the characters `OK'.
The ELM624's factory default settings should be
appropriate for most applications, but some users may
wish to customize their settings, such as turning the
character echo off or linefeed generation on by issuing
these commands.
The following summarizes the `AT' commands that
are recognized by the current version of the ELM624
(commands not supported by the older version 1.0
software are as noted). Note that the character `0' is
the number `zero':
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 bytes, while with C0
the response bytes 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, so they do continually
change. The default is C1, send on change.
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. Issuing ATD1 will force the words in
bytes 0 and 1 to be duplicated in bytes 2 and 3. The
default is D1, duplicate on.
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, and perhaps simplify some
computer software, users may wish to turn echoing
off by issuing E0. The default is E1, echo on.
ATI
This causes the IC to identify itself. On receiving this
command, it will send the power-on identifying
message (currently `ELM624 v2.0') and will then
return to the ready mode.
ATL0 and ATL1
Whether or not the ELM624 transmits a linefeed
character when a carriage return character is sent, is
controlled by this option. If an ATL1 is issued,
linefeed generation will be turned on, and for ATL0
(the default) it will be off. Users may wish to have
this option turned on to improve readability if their
terminal program does not offer it, but should leave it
off if using computer control (as the extra characters
transmitted will only serve to slow the system down).
Not supported by version 1.0 software.
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 to the Control L device
multiple times. While the Control L standard requires
that commands must be repeated at least four
consecutive 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 (an R0 is treated as an R1).
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.
AT?
This is a useful way to quickly obtain the current
status bytes from the LANC device without having to
wait while the ELM624 issues a command. This can
be of advantage in cases where several devices are
interconnected, and you wish to sequentially poll
each device to determine its status. Not supported
by version 1.0 software.
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