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2.1 At-commands Basic Example
AT is the abbreviation of ATtention .AT commands also called
Hayes command .At command is used to
control modem. The AT command is a Command Prompt command which is used to schedule other
commands and programs to run at specific dates and times.
WHAT IS MODEM?
MODEMS are used from a long time .The word MODEM is a
combination of MODULAR and
DEMODULAR. A modem is a device or program that enables a computer to transmit data over, for example,
telephone or cable lines. A MODEM converts data in two forms
digital and analog.
Computer information is stored digitally whereas information transmitted over telephone lines is
transmitted in the form of analog waves. Digital data coming from a DTE, data
terminal equipment is modulated
in such a way that it can be sent over transmission lines. On the other side
another modem demodulates
the incoming data and forwards them. Modem keeps everyone connected, over
the Internet technology.
There are two types of MODEM used :
1.Internal modem:-These modems are installed inside the
PC or Laptop. allowing to communicate with other computer over the network. internal modems are further divided into two categories.
Dial-up and WI-FI (wireless).internal modems also called built in modems or PC card modem.
Internal computer modems are used with Dial-Up Internet connection through a couple of RJ-11 connection. Also called copper telephone lines,
the RJ-11 allows computer to receive and send data Internal computer modemsare usually 56K modems which mean that the modem is able
to receive 56 Kbps (56 kilobits or 56000 bits per second) of data.
2.External modem:-External modem is a small box that can
used other interfaces to connect to the computer. The purpose of external
modem is same as internal modem. serial modem
is one of the external modem it called serial because it uses serial port to
connect to the computer.other external modem is
which is also a small box it connect to the USB port. Another type of
external modem that may consider two important types of modem: cable modem and DSL modem. Cable
modems is a type of modem that allows people to access the Internet via
their television service. DSL (Digital
Subscriber Line) modem is used for connections from a
telephone switching office to the user. DSL modem is a device used to connect a
single computer or router to a DSL phone line. service. Another example of external modem is GSM modem. A GSM modem can
be an external unit . An external GSM modem is connected to a PC through a serial cable,
a USB cable, Bluetooth or Infrared. Like a GSM mobile phone, a GSM modem requires a SIM card from a wireless carrier in order to operate.
PC use AT command to control modem.
WHY USE AT-command?
AT command are instructions used to control modem. Every command
line on command prompt for modem start with "AT" or "at "command.therefore modem commands are called AT commands. There are
two type of AT command.
Basic command and:-Basic AT commands are those
commands which are not started with "+".sign.for example D (dial) , A (answer) ,H
(hook), and O (return to the online data state) are basic AT
Extended commands:-These commands are start with
"+" sign.all GSM AT commands are extended commandsSome commands that are used to control wired dial-up modems are:
For example, +CMGS (Send SMS message),
+CMSS (Send SMS message from storage),
+CMGL (List SMS messages) and +CMGR (Read
SMS messages) are extended commands.
GENERAL SYNTAX OF AT COMMAND
At command prompt all command lines must start with
"AT" and end with a carriage return character<CR>.In case
of Microsoft Windows, you can press the Enter key on the keyboard to output a
carriage return character.
EXAMPLE :-AT+CMGL<CR> here <CR> is the courge return
SOME AT COMMANDS FOR GSM?GPRS
MODEM OR MOBILE PHONE
Here are some of the tasks that can be done using AT commands
with a GSM/GPRS modem or mobile phone:
Commands to get the basic information about the mobile phone
or GSM/GPRS modem.
AT+CGMI used to the name of the manufacturer.
AT+CGMM used to get the model number.
AT+CGSN to get the IMEI (international mobile equipment
identity) number of equipment.
AT+CGMR to get the software version 2.Commands to get the basic information about the subscriber.
(AT+CIMI). to get IMSI number (International Mobile
Subscriber Identity)3. To get the current status of the mobile phone or GSM/GPRS
(AT+CPAS) to know the mobile phone activity status.
(AT+CREG) to know the mobile phone registration status.
(AT+CSQ) to know the radio signal strength.4.At command to send and receive
fax Send and receive fax
(ATD, ATA, AT+F*).At command to read ,write ,search phone book.
Read (AT+CPBR), write (AT+CPBW), or search (AT+CPBF)
phonebook entries. AT command to Save and restore configurations of the mobile
phone or GSM/GPRS modem.
save (AT+CSAS) and restore (AT+CRES) settings
related to SMS messaging such as the SMS center address
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