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SI2401

V.22BIS ISOMODEM® WITH LOW-COST DAA

Silicon Laboratories 

Si2401/Si3008

Table 12. AT Command Set Summary

q#

Read S-Register in binary

V0

Result code with no carriage return

V1

Result code with added carriage

returns

Z

Software reset

z

Wakeup on ring

5.3. AT Command Set Description

A

Answer

The “A” command makes the modem go off-hook and

respond to an incoming call. This command is to be

executed after the Si2401 has indicated a ring has

occurred. (The Si2401 indicates an incoming ring by

echoing an “R”.)

This command is aborted if any other character is

transmitted to the Si2401 before the answer process is

completed.

Auto answer mode is entered by setting S00 (NR) to a

non-zero value. NR indicates the number of rings before

answering the line.

Upon answering, the modem communicates by

whatever protocol has been determined via the modem

control registers in S07 (MF1).

If no transmit carrier signal is received from the calling

modem within the time specified in S39 (CDT), the

modem hangs up and enters the idle state.

D

Dial

DT#

Tone Dial Number.

DP#

Pulse Dial Number.

The D commands make the modem dial a telephone

call according to the digits and dial modifiers in the dial

string following the command. A maximum of 64 digits is

allowed. A DT command performs tone dialing, and a

DP command performs pulse dialing.

The ATH1 command can be used to go off-hook without

detecting a dial tone or dialing.

The dial string must contain only the digits “0–9”, “*”, “#”,

“A”, “B”, “C”, “D”, or the modifiers “;”, “/”, or “,”. Other

characters are interpreted incorrectly. The modifier “,”

causes a two-second delay (added to the spacing value

in S04) in dialing. The modifier “/” causes a 125 ms

delay (added to the spacing value in S04) in dialing. The

modifier “;” returns the device to command mode after

dialing and must be the last character.

If any character is received by the Si2401 between the

ATDT#<CR> (or ATDP#<CR>) command and when the

connection is made (“c” or “d” is echoed), the extra

character is interpreted as an abort, and the Si2401

returns to command mode ready to accept AT

commands. A line feed character immediately following

the <CR> is treated as an “extra character” and aborts

the call.

If the modem does not have to dial (i.e., “ATDT<CR>” or

“ATDP<CR>” with no dial string), the Si2401 assumes

the call was manually established and attempts to make

a connection.

5.3.1. Automatic Tone/Pulse Dialing

The Si2401 can be configured to attempt DTMF dialing

and automatically revert to pulse dialing if it determines

that the line is not DTMF-capable. This feature is best

explained by the following example:

If it is desired that the telephone number, 12345, be

dialed, it is normally accomplished through either the

ATDT12345 or the ATDP12345 command. In the force

pulse dialing mode of operation, the following string

should be issued instead:

ATDT1,p12345

A result code of “t,” indicates that the dialing was

accomplished using DTMF dialing. If the result code

returned is “tt,”, this indicates that the dialing was

accomplished using pulse dialing.

In the above example, the Si2401 dials the first digit “1”

using DTMF dialing. The “,” is used to pause in order to

ensure that the central office has had time to accept the

DTMF digit “1”. When the Si2401 processes the “p”

command, it attempts to detect a dial tone. If a dial tone

is detected, the DTMF digit “1” was not effective, hence,

the line does not support DTMF dialing. Conversely, if

the dial tone is not detected, the DTMF digit “1” was

effective, and the line supports DTMF dialing. The

character after the “p” may or may not be dialed

depending on whether the DTMF digit “1” was effective

or not. If the “1” was effective (DTMF mode), the

character after the “p” is skipped. The next DTMF digit

to be dialed is “2”. Subsequent digits are all DTMF. If the

“1” was not effective, the first character after the “p” (the

“1”) is pulse dialed, and subsequent digits are all pulse

dialed.

E

Command Mode Echo

Tells the Si2401 whether or not to echo characters sent

from the terminal.

EO

Does not echo characters sent from the terminal.

E1

Echoes characters sent from the terminal.

H0

Hangup

Hang up and go into command mode (go offline).

Rev. 1.1

21

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