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ELM633SM Datasheet(PDF) 4 Page - ELM Electronics |
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ELM633SM Datasheet(HTML) 4 Page - ELM Electronics |
4 / 11 page AT Commands The ELM633 is controlled with short commands that all begin with the two characters ‘AT’ (which is short for ATtention). These two characters serve no purpose other than to help add validity to the characters that follow. Modem manufacturers have used this same technique for years, and it has become customary to refer to commands that begin with these characters as ‘AT Commands’. The ELM633 accepts several different AT commands, but only one at a time (it cannot process multiple commands on one line, as most modems can). Each is executed only upon receipt of the terminating carriage return character. Several commands do not have a visible response (AT D for example), so completion of those commands will be 4 of 11 ELM633 ELM633DSB Elm Electronics – Circuits for the Hobbyist < http://www.elmelectronics.com/ > Communicating with the ELM633 The ELM633 relies on a standard RS232 serial connection to communicate with the user. The data rate is not adjustable and is set at 57600 baud, with 8 data bits, no parity bit, 1 stop bit, and no handshaking (often referred to as 57600 8N1). All responses from the IC are terminated with a single carriage return character and, optionally, a linefeed character. Make sure your software is configured properly for this connection (and the linefeed mode that you have chosen). No special software is required to ‘talk’ to the IC – a standard terminal program is all that is needed. Once it has been properly connected and powered, the ELM633 will send the message: ELM633 v2.0 > In addition to identifying the version of this IC, receiving this string is a good way to confirm that the computer connections and terminal software settings are correct. The ‘>’ character displayed above is the ELM633’s prompt character, which shows that the device is in its idle state, ready to receive characters on the RS232 port. All messages that are sent to the ELM633 must begin with the character ‘A’ followed by the character ‘T’, and must be terminated with a carriage return character. No action is taken – commands are not checked for errors, nor are they acted upon – until this terminating carriage return is received. The one exception is when a command is interrupted for some reason, and no carriage return appears. In this case, an internal timer will automatically abort the incomplete message after about 15 seconds, and the ELM633 will print a single question mark to show that the input was not understood (and was not acted upon). Messages that are not understood by the ELM633 (syntax errors) will always be signalled by this same single question mark (‘?’). When this occurs, it is usually due to a spelling mistake, so you often only need to repeat the input, typing more carefully. Occasionally, errors occur if the ELM633 is busy processing LIN messages when an RS232 command message begins. In these cases, the first character of the RS232 command message will always be missed by the IC, so the remaining characters will appear to be incorrect. You should always interrupt the monitoring process with a single character (it doesn’t matter which one, as it will be ignored), then wait for the prompt character (“>”) to appear before sending any more. This ensures that the ELM633 is ready to receive commands. For convenience, the ELM633 has been designed to ignore spaces and control characters in the input, so if you prefer to add spaces, tabs, etc., to improve readability, then go ahead. Also, the ELM633 is not case-sensitive, so ‘ATZ’ is equivalent to ‘atz’ and to ‘AtZ’, which may be helpful for some people. acknowledged by the printing of the characters ‘OK’. Monitoring of the LIN bus can generally begin without requiring the use of any AT commands, as the factory default settings should be appropriate for most situations. Occasionally, however, the user may wish to customize settings, such as turning the character echo off, and in these cases, AT commands must be used. To perform the desired AT command, simply send the characters AT followed by the appropriate characters from the following list. For example, to turn character echoing off, simply send AT E0 followed by a return character. To turn it back on, send AT E1. The following is a summary of the commands that are recognized by the current version of the ELM633. |
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