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AT S18 = 0 &T1 Causes the modem to run local analog loopback without self-test. CONNECT 115200 Modem response code indicates that analog loopback is enabled with a DTE speed of 115200. This is a test. Test string that the user could type at the keyboard. If the received data is Intel Confidential Programmer’s Guide 56K V.92 Data, Fax, and Voice Chipset the same as the test string, then the DTE-to-modem communication channel is working properly. +++AT TIES Escape Sequence is used to return to command mode. OK Modem enters command mode. AT&T0 Terminates any loopback test. OK Modem aborts analog loopback and stays in command mode. Programmer’s Guide Intel Confidential 56K V.92 Data, Fax, and Voice Chipset 3.9.2 Local Analog Loopback With Self-Test [AT&T8] This test is used by the local DTE to check the DTE-to-modem communication integrity. DTE TXD RXD TRANSMITTER RECEIVER LOCAL MODEM PATTERN GENERATOR PATTERN CHECKER Figure 3-3. Local Analog Loopback with Self-Test Local Modem (or Test Modem) AT&F &W Returns the modem to the factory defaults. AT S18=20 &T8 Causes the modem to start local analog loopback with self-test for 20 seconds. OK After starting analog loopback, the modem goes back to command mode. AT The modem responds to new commands. OK 000 After 20 seconds, the modem stops analog loopback, sends OK An error count to the DTE, and enters command mode. AT S18=0 &T8 Causes the modem to start local analog loopback with self-test, which is only terminated by AT&T0 or ATH. OK After starting analog loopback, the modem goes back to command mode. AT The modem responds to new commands. OK AT&T0 After receiving AT&T0 or ATH, the modem stops analog 000 loopback, sends an error count to the DTE, and enters Intel Confidential Programmer’s Guide 56K V.92 Data, Fax, and Voice Chipset OK command mode. 3.10 AT Escape Sequences The 56K family provides the industry-standard Time Independent Escape Sequence (TIES). The DTE sends the escape sequence to return the modem to command state while in the online data state (that is, connected to another modem) or in diagnostic mode (&Tn commands). Intel also makes the Hayes. Escape Sequence available to customers; however, see the following statement regarding licensing requirements. Licensing Requirements for Hayes Escape Sequence The Intel 56K FastPath chipsets are manufactured with TIES as the default setting. It is Hayes’ position that you must either have or obtain a valid license from Hayes Microcomputer Products, Inc., of Norcross, Georgia, before producing modem systems that use the Hayes Escape Sequence. Intel accepts no responsibility and does not indemnify nor in any way provide protection for patent or possible patent violations to its customers or users of its products. 3.10.1 Time-Independent Escape Sequence The TIES (Time-Independent Escape Sequence), implemented with +++AT, was developed by a group of modem manufacturers as an alternative to the Hayes Escape Sequence. TIES was designed for compatibility with existing communication software written for the Hayes Escape Sequence. 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 ). 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: 1) 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). a) 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. b) 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 , or up to 39 data characters, before deciding whether to go to command mode or to return to data mode. Upon detecting a or receiving the 39 data characters, the modem determines if a valid AT command has been received. If a non-AT command string or an invalid command string has been received, then the modem changes back to data mode and sends a “CONNECT” message to the DTE. If a valid AT command has been received, the modem changes to Programmer’s Guide Intel Confidential 56K V.92 Data, Fax, and Voice Chipset command mode and sends an ‘OK’ message. After sending the “OK” message, the modem echoes any received data from the DTE while in command mode. 2) An “A” or “a” is received from the DT...

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