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Interfacing GSM Modem

With Microcontroller

By: Gaurav Arora


2/22

Building a Embeded system with ability to SendSms using an GSM modem.

b!ective


3/22

W"# $%W

Initiali&e system to set 'arameters fortransmission and interru't

System waits to be triggred using a sensor or

an manual E(ternal interru't li)e Switch. *etecting interru't Atmega +, -hec)s

availability of modem and tries to send SMS

using GSM Modem using A -ommands.


4/22

*efining Modules

System -onsist of three modules:

>Interru't *etection.

> Activating /SA" module ransmittingand "eceving *ata.

> Sending A commands to GSM Modem.


5/22

GSM M*EM

A GSM modem is a wireless modem that wor)swith a GSM wireless networ).

A commands are used to control modems.

'erations 0erformed by GSM Modem.

"eading1 writing and deleting SMS messages.

Sending SMS messages.

"eading1 writing and searching 'hone boo) entries.

GSM Modem *atasheet : ++223datasheet.'df inyour )it


6/22

-onfiuring GSM Modem

4 Insert SIM card: 0ress the yellow 'in to remove thetray from the SIM cardholder. insert SIM card

Connect RS232 Cable: 5-able 'rovided for "S262

communication7 *efault baud rate is 8,995using2997

with ;


7/22

Some erms

BA/* "AE


8/22

A commands

A is the abbreviation of Atention.

A commands are instructions used to control amodem.

A commands used to send SMS

A


9/22

Interfacing Modem withMicrocontroller


10/22

ut'ut of hy'er


11/22

/SA"

/SA" < /niversal synchronous and asynchronous receiverand transmitter.

Main "egisters /-S"A1/-S"B1/-S"-1/B""1/*"

/-S"( /SA" -ontrol and Status "egister A1B1-.

/B"" /SA" Baud rate "egister

/*" /SA" *ata "egister.

wo /*" /SA" register to transmit and receive to 'rovidefull du'le( mode.

Must "ead Status Bits before receiving or transmitting *ata5most im'ortant7

>- and ">- flags.


12/22

Initiali&ing/SA" module


13/22

Activating /SA" module5+7

we have to enable the /A" "eceiver andransmitter using bit ">E= and >E= in

/-S"B register


14/22

Activating /SA" module527

Bit 6 >E=: ransmitter Enable

Writing this bit to one enables the /SA" ransmitter. heransmitter will override nor


15/22

Activating /SA" module567

Setting Baud "ate:

Set values of /B""


16/22

/SA" initiali&ation code

/B""H@9(99

/B""% @ 5unsigned char7Baud"ate J Set thebaud rate J

/-S"B @ 9b999++999 enable transmitter andreciever

/-S"- @ 9b+9999++9 ; bit data1 no 'arity bit1

+ sto' bit.


17/22

/SA" ransmission

In /-S"A register Bit ? /*"E: /SA" *ata"egister Em'ty

he /*"E flag indicates if the transmit buffer 5/*"7 is

ready to receive new data. If /*"E is one1 the buffer is em'ty1 and therefore ready to

be written.

If /*"E is one 'ut data in the buffer.


18/22

0roblem with Baud rates

GSM modem su''orts a wide range of baudrates ++29


19/22

/SA" "E-E0I=

In /-S"A register bit L: Bit L ">-: /SA" "eceive-om'lete

his flag bit is set when there are unread data in thereceive buffer and cleared when thereceive buffer isem'ty 5i.e.1 does not contain any unread data7.


20/22

Interru't *etection

-ode sni'lets used to set Interru't.

GI-" @ 9(9 enable e(ternal interru't 9

M-/-" @ 9(92 activate e(ternal interru't9 5on 'in+,7it recogni&es rising edge

sei57set enable interru'ts.

If e(ternel interru'ts is 'rovided to system then controlgoes to interru't handler and set a flag variable to one.

And send the reKuired Sms.


21/22

Have a loo) on codeNN Any OuestionsPP


22/22

han) QouN

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