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ELM624P

Control L (LANC) to RS232 Interpreter

Elm Electronics 

ELM624

Overview

The following describes how to use the ELM624 to

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,

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…

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.

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

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.

ELM624DSD

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

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