Data Mode AT COMMANDS
The DTE implements the escape sequence by sending the escape character (as defined in S2) three times, followed by a valid AT command, and then the contents of S3 (typically a <CR>). Upon detecting the three consecutive escape characters, the modem changes to TIES command mode and starts an internal EPD (Escape Prompt Delay) timer (with the time limit defined by S12). The modem then looks for one of the following conditions to occur:
•No additional data is received and the EPD timer times out: the modem sends an ‘OK’ message to the DTE and then waits indefinitely for an incoming valid AT command string from the DTE. Until the modem receives a valid AT command, it monitors any data received from the DTE and passes on the data to the remote modem (that is, the modem does not echo back the received character to the DTE).
—If the subsequent character received by the modem is not an ‘A’ or ‘a’, the modem returns to data mode and sends a ‘CONNECT’ message back to the DTE.
—If the modem receives an ‘A’ or ‘a’, it stores any additional data received from the DTE in the modem’s internal command buffer and continues to send the data to the remote modem. The modem then waits until the DTE sends a <CR>, or up to 39 data characters, before deciding whether to go to command mode or to return to data mode. Upon detecting a <CR> or receiving the 39 data characters, the modem determines if a valid AT command has been received. If a
•An ‘A’ or ‘a’ is received from the DTE. The modem disables the EPD timer and sends the character to the remote modem. The modem then stores any received data from the DTE into the modem internal command buffer and sends the data to the remote modem. Upon detecting a <CR> or receiving up to 39 data characters, the modem determines if a valid AT command has been received; if so, it processes the valid commands. If a
•Any character except an ‘A’ or ‘a’ is received from the DTE. The modem disables the EPD timer and changes back to data mode.
If an AT command string is received while in TIES command mode, the modem processes any valid AT command. Upon detecting an invalid AT command, the modem changes back to data mode and issues a ‘CONNECT’ message to the DTE. While in TIES command mode, the modem ignores certain characters that may cause the modem to incorrectly decide that an incoming AT string is invalid. The ignore characters are <LF>, <space>, and <CR> (<CR> is ignored only when S3 is not equal to <CR>). Not all AT commands are supported during TIES command mode. The following is a list of supported commands:
En, Hn, Mn, On, Qn, Sn, Vn, Xn, and ‘&’ commands (except &Tn and &F)
The escape character is determined by the value stored in
Format:
<char1><char2><char3><AT command><contents of S3>
char1 = char2 = char3 = escape character (S2)
Example:
536EX Chipset Developer’s Manual | 39 |
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