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SI2401

V.22BIS ISOMODEM® WITH LOW-COST DAA

Silicon Laboratories 

Si2401/Si3008

5. AT Command Set

The controller provides several vital functions including

AT command parsing, DAA control, connect sequence

control, DCE protocol control, intrusion detection,

parallel phone off-hook detection, escape control, caller

ID control and formatting, ring detect, DTMF control, call

progress monitoring, and HDLC framing. The controller

also writes to the control registers that configure the

modem. Virtually all interaction between the host and

the modem is done via the controller. The controller

uses AT (ATtention) commands and S-Registers to

configure and control the modem.

The modem has two modes of operation: command

mode and data mode. The Si2401 is asynchronous in

both command mode and data mode. The modem is in

command mode at powerup, after a reset, before a

connection is made, after a connection is dropped, and

during a connection after successfully “Escaping” from

the data mode back to the command mode using one of

the methods previously described. The following section

describes the AT command set available in command

mode.

The Si2401 supports a subset of the typical modem AT

command set since it is intended for use with a

dedicated microcontroller instead of general terminal

applications. AT commands begin with the letters AT

and are followed directly (no space) by the command.

These commands are also case-sensitive. All AT

commands must be entered in upper case including AT

except w##, r#, m#, q#, and z (wakeup-on-ring).

AT commands can be divided into two groups: control

commands and configuration commands. Control

commands, such as ATD, cause the modem to perform

an action (going off-hook and dialing). The value of this

type of command is changed at a particular time to

perform a particular action. For example, the

ATDT1234<CR> command causes the modem to go off

hook and dial the number, 1234, via DTMF. This action

exists only during a connection attempt. No enduring

change in the modem configuration exists after the

connection or connection attempt has ended.

Configuration commands change modem

characteristics until they are modified or reversed by a

subsequent configuration command or the modem is

reset. Modem configuration status can be determined

with the use of “ATSR?<CR>” Where R is the two-

character hexadecimal address of an S-register.

A command line is defined as a string of characters

starting with AT and ending with an end-of-line

character, <CR> (13 decimal). Command lines may

contain several commands one after the other. If there

are no characters between AT and <CR>, the modem

responds with “O” after the carriage return.

5.1. Command Line Execution

The characters in a command line are executed one-at-

a-time. Unexpected command characters are ignored,

but unexpected data characters may be interpreted

incorrectly.

After the modem has executed a command line, the

result code corresponding to the last command

executed is returned to the terminal or host. In addition

to the “ATH” and “ATZ” commands, the commands that

warrant a response (e.g., “ATSR?” or “ATI”) must be the

last in the string and followed by a <CR>. All other

commands may be concatenated on a single line. To

echo command line characters, set the Si2401 to Echo

mode using the E1 command.

All numeric arguments, including the address and value

of an S-register, are in hexidecimal format, and two

digits must always be entered.

5.2. <CR> End-Of-Line Character

This character is typed to end a command line. The

value of the <CR> character is 13 in decimal, the ASCII

carriage return character. When the <CR> character is

entered, the modem executes the commands in the

command line.

Note: Commands that do not require a response are exe-

cuted immediately and do not need a <CR>.

Table 12. AT Command Set Summary

Command

A

DT#

DP#

E

H0

H1

I

:I

M

O

RO

S

w##

r#

m#

Function

Answer line immediately with modem

Tone dial number

Pulse dial number

Local echo on/off

Go on-hook (hang up modem)

Go off-hook

Chip revision

Interrupt read and clear

Speaker control options

Return online

V.23 reverse

Read/write S-Registers

Write S-Register in binary

Read S-Register in binary

Monitor S-Register in binary

20

Rev. 1.1

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