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ELM322 Datasheet(PDF) 5 Page - ELM Electronics |
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ELM322 Datasheet(HTML) 5 Page - ELM Electronics |
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5 / 18 page  5 of 18 ELM322 ELM322DSE Elm Electronics – Circuits for the Hobbyist < http://www.elmelectronics.com/ > AT Commands Several parameters within the ELM322 can be adjusted in order to modify its behaviour. These do not normally have to be changed before attempting to talk to the vehicle, but occasionally the user may wish to customize the settings, for example by turning the character echo off, adjusting the timeout value, or changing the header addresses. In order to do this, internal ‘AT’ commands must be issued. Those familiar with PC modems will immediately recognize AT commands as a standard way in which modems are internally configured. The ELM322 uses essentially the same method, always watching the data sent by the PC, looking for messages that begin with the character ‘A’ followed by the character ‘T’. If found, the next characters will be interpreted as internal configuration or ‘AT’ commands, and will be executed upon receipt of a terminating carriage return character. The ELM322 will reply with the characters ‘OK’ on the successful completion of a command, so the user knows that it has been executed. Some of the following commands allow the passing of numbers as arguments in order to set the internal values. These numbers will always be in hexadecimal format, and must be provided in pairs. The hexadecimal conversion chart in the next section may prove useful if you wish to interpret the values. Also, one should be aware that for the on/off types of commands, the second character will be either the number 1 or 0, the universal terms for on and off. The following is a summary of all of the AT commands that are recognized by the current version of the ELM322, sorted alphabetically. Users of previous versions of this product (v1.x) should note that their ICs will only support the E, H and Z options. AR [ Automatically set the Receive address ] Responses from the vehicle will be acknowledged and displayed by the ELM322, if its internally stored receive address matches the address that the message is being sent to. With the Auto Receive mode in effect, the value used for the receive address will be chosen based on the current header bytes, and will automatically be updated whenever the header bytes are changed. The value that is used for the receive address is determined based on the contents of the first header byte. If it shows that the message uses physical addressing, the third byte of the header is used for the receive address, otherwise (for functional addressing) the second header byte, increased in value by 1, will be used. Auto Receive is turned on by default. D [ set all to Defaults ] This command is used to set the E, H, L, and R options to their default (or factory) settings, as when power is first applied. Additionally, the Auto Receive mode (AR) will be selected, data will be transmitted in the standard formatted way (as if chosen by FD), the ‘NO DATA’ timeout will be set to its default value, and the header bytes will be set to the proper values for OBDII (SAE J1979) operation. E0 and E1 [ Echo off (0) or on (1) ] These commands control whether or not 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 ATE0. The default is E1 (echo on). FD [ send Formatted Data ] This command requests that all responses be returned as standard ASCII characters, which are readable with virtually any terminal program. Hex digits are shown as two ASCII characters, and spaces are provided between each byte as a separator. Also, every line will end with a carriage return character and (optionally) a linefeed character, ensuring that every response appears on a new line. This is the default mode. H0 and H1 [ Headers off (0) or on (1) ] These commands control whether or not the header information is shown in the responses. All OBD messages have an initial (header) string of three bytes and a trailing check digit which are normally not displayed by the ELM322. To see this extra information, users can turn the headers on by issuing an ATH1. The default is H0 (headers off). |
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