Intel MD566X 3.10 AT Escape Sequences

56K V.92 Data, Fax, and Voice Chipset

Programmer’s Guide Intel Confidential 39

OK comma nd 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.

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 <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:

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 com-

mand string from the DTE. Until the modem receives a valid AT command, it moni-

tors 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 d ata 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 sen ds 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 da ta char-

acters, 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

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.