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ELM329 Datasheet(PDF) 11 Page - ELM Electronics |
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ELM329 Datasheet(HTML) 11 Page - ELM Electronics |
11 / 76 page 11 of 76 ELM329 ELM329DSB Elm Electronics – Circuits for the Hobbyist www.elmelectronics.com AT Command Descriptions <CR> [ repeat the last command ] Sending a single carriage return character causes the ELM329 to repeat the last command that it performed. This is typically used when you wish to obtain updates to a value at the fastest possible rate - for example, you may send 01 0C to obtain the engine rpm, then send only a carriage return character each time you wish to receive an update. . [1 - 8 bytes] [ send message with 11 bit ID ] Sending a single period (‘.’) followed by 1 to 8 data bytes will cause the ELM329 to send those data bytes along with the currently defined 11 bit ID. The data will be sent exactly as provided - no formatting bytes or filler bytes will be added, and the number of data bytes sent will be the same as what you provide (so if you need to send 8 bytes as for ISO 15765, then you must provide all 8). The default value used for the 11 bit ID is 7DF, but this may be changed with the AT SH xyz command. A protocol must be active before you can use this command, as the ELM329 needs to know the current baud rate, etc. You may always send an 11 bit ID message with this command, even if the currently active protocol uses a 29 bit ID. : [1 - 8 bytes] [ send message with 29 bit ID ] Sending a single colon (‘:’) followed by 1 to 8 data bytes will cause the ELM329 to send those data bytes along with the currently defined 29 bit ID. The data will be sent exactly as provided - no formatting bytes or filler bytes will be added, and the number of data bytes sent will be the same as what you provide (so if you need to send 8 bytes as for ISO 15765, then you must provide all 8). The default value used for the 29 bit ID is 18 DB 33 F1, but this may be changed with the AT SH xxyyzz or AT SH wwxxyyzz commands. A protocol must be active before you can use this command, as the ELM329 needs to know the current baud rate, etc. You may always send a 29 bit ID message with this command, even if the currently active protocol uses an11 bit ID. AT0, AT1 and AT2 [ Adaptive Timing control ] After an OBD request has been sent, the ELM329 waits to see if any responses are coming from the vehicle. The maximum time that it waits is set by the AT ST hh setting, but this setting is purposely a little longer than it needs to be, in order to ensure that the IC will work with a wide variety of vehicles. Although the setting is adjustable, many people do not have the equipment or experience that it would take to determine an optimal value. The Adaptive Timing feature automatically sets the timeout value for you, to a value that is based on the actual response times that your vehicle is responding in. As conditions such as bus loading, etc. change, the algorithm learns from them, and makes appropriate adjustments. Note that it always uses your AT ST hh setting as the maximum setting, and will never choose one which is longer. There are three adaptive timing settings that are available for use. By default, Adaptive Timing option 1 (AT1) is enabled, and is the recommended setting. AT0 is used to disable Adaptive timing (so the timeout is always as set by AT ST), while AT2 is a more aggressive version of AT1 (the effect is more noticeable for very slow connections – you may not see much difference with faster OBD systems). The J1939 protocol does not support Adaptive Timing – it uses fixed timeouts as set in the standard. BD [ perform an OBD Buffer Dump ] All messages sent and received by the ELM329 are stored temporarily in a set of twelve memory storage locations called the OBD Buffer. Occasionally, it may be useful to see the contents of this buffer, perhaps to see why a request failed, to see the header bytes in the last message, or just to learn more of the structure of OBD messages. You can ask at any time for the contents of this buffer to be ‘dumped’ (ie printed). When you do, the ELM329 sends a length byte (representing the length of the current message in the buffer) followed by the contents of all twelve OBD buffer locations. For example, here’s one ‘dump’: The following describes each AT Command that the current version of the ELM329 supports, in a little more detail. Many of these commands are also described further in other sections: |
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