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ELM624DSB Datasheet(PDF) 4 Page - ELM Electronics |
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ELM624DSB Datasheet(HTML) 4 Page - ELM Electronics |
4 / 7 page 4 of 7 ELM624 ELM624DSB 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 that begins with the characters A followed by T is considered an internal configuration or ‘AT’ command. These are executed upon receipt of the terminating carriage return character, and acceptance of a command is acknowledged by the printing of the characters ‘OK’. The factory default settings should be sufficient for most applications, and communications on the LANC port can generally begin without requiring the issuance of any AT commands, but some users may wish to customize settings, such as turning the character echo off, etc. The following summarizes the ‘AT’ commands that are recognized by the ELM624. Note that the character ‘0’ is the number ‘zero’: Communicating with the ELM624 The ELM624 relies on a standard RS232 type serial connection to communicate with the user. All commands are sent to, and responses are received from the ELM624 over this interface. The RS232 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). Properly connected and powered, the ELM624 will initially display the message: ELM624 v1.0 (c)1999 In addition to identifying the version of the IC, receipt of this string is a convenient way for users to be sure that their connections are correct. After displaying this message, the integrated circuit will be ready for a command on the RS232 port, and will wait indefinitely until a valid one is received. Commands can either be for internally configuring the ELM624, or for passing on to the LANC port. The internal commands are distinguished by always beginning with the characters ‘AT’, while the two Control L bytes are simply a series of four hex digits. See the following sections for further details. Some other characteristics to note concerning the commands are that extra characters are not permitted (spaces, tabs, etc.), all commands must be terminated with a carriage return character (hex ‘0D’), and the ELM624 is not case-sensitive (so ‘ATZ’ is equivalent to ‘atz’, as is ‘AtZ’). Understood and executed ‘AT’ commands are signalled by the transmission of the two characters ‘OK’, while any misunderstood commands (syntax errors) are signalled by a single question mark (‘?’) being sent. When Control L commands are executed, correct completion is signalled by the ELM624 transmitting the four status bytes received from the LANC bus (sent as eight hexadecimal digits). To reduce RS232 traffic, all responses are terminated with a single carriage return character, and no line feed character. Some users may wish to have their software insert these linefeed characters to improve readability. There is a possibility that incomplete data strings could be sent to the ELM624 for one reason or another. To avoid problems in these cases, the ELM624 will automatically time out and abort any incomplete command after about 20 seconds. It will then print a single question mark, and wait for the next command to be sent. One last note involves the internal priorities assigned to the two busses. In all cases, the RS232 bus takes priority over the LANC bus, and will cause any LANC transmissions to abort if activity is detected on the RS232 bus. 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, while with C0 they 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, thus continually change. The default is C1. 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’, while setting D1 will force the words to be duplicated. The default is D1. |
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