1 GSM MODEM :

INTRODUCTION:What is GSM?

GSM stands for Global System for Mobile Communication. It is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz.

Functions – GSM Modes

Table 3.1.1: Functions – GSM Modes

The GSM modem basically consists of a SIM card holder to hold the activated SIM card for sending and receiving SMS. 5V AC power supply header to which the 5v ac adapter is connected. Power led which gives the indication of modem status that is on or off. 9 pin female to which the GSM antenna is connected.

Block Diagram of GSM:

TA TE ME

Fig 3.1.1 : GSM Modem Block Diagram

GSM Network Setup:

USER & APPLICATIONS NETWORK

Fig 3.1.2 :GSM setup

This is the basic setup of a GSM. Here ME stands for Mobile Equipment, e.g. a GSM phone (equal to MS; Mobile Station). TE stands for Terminal Equipment, e.g. a computer (equal to DTE; Data Terminal Equipment). TA stands for Terminal Adaptor, e.g. a GSM data card (equal to DCE; Data Circuit Terminating Equipment). Through the mobile equipment the network messages are sent and received. These messages are sent to the terminal adapter which is nothing but a GSM data card. Now if there is some data to be sent to the mobile equipment then the terminal equipment that is basically a computer or processor sends out AT COMMANDS to the terminal adapter which in turn sends the mobile equipment the required data as shown in fig 3.1.2

Connection Diagram:

The GSM modem being a serial communication device is connected to the serial port or a serial device through a serial connector. The power input to the modem is given through a 9v ac adapter as shown in fig 2.2

Fig 3.1.3 : Connection Diagram

LED Status Indicator

The LED will indicate different status of the modem:

- OFF Modem Switched off- ON Modem is connecting to the network- Flashing Slowly Modem is in idle mode- Flashing rapidly Modem is in transmission/communication (GSM only)

GSM SPECIFICATIONS:Before looking at the specification, it is important to understand the following basic terms:Bandwidth: The range of channels limits, the broader the bandwidth, the faster the data can be sent.Bits per second (BPS): A single on-off pulse of data. Eight bits are equivalent to one byte.Frequency: The number of cycles per unit of time. It is measured in hertz.Watt (W): A measure of power of transmitter.Frequency band: The frequency rage specified for GSM is 1850 to 1990 MHz.Duplex Distance: The duplex distance is 80 MHz. The duplex distance is the distance between uplink and downlink frequencies. A channel has two frequencies 80 MHz a part.Channel Separation: The separation between adjacent carrier frequencies is 200 KHz.Transmission rate: GSM is a digital system with the over the air bit rate of 270 Kbps.

9-PIN D-SUB Female Connector:

PIN NAME DESIGNATION TYPE

1 X None NC NC2 Tx Transmit Data Input3 Rx Receive Data Output4 DSR Data Set Ready Output5 GND Ground Ground6 DTR Data Terminal Ready Input7 CTS clear to send Output8 RTS Request to send Input9 X None NC NC

Table 3.1.2 : PIN D-SUB Female Connector

GSM (Global System for Mobile Communication) :

Open the Package directory from the CD and run the setup.exe file to start the installation.

Once “Welcome to the Smart Modem Installation Program” appears on screen, click the “OK” button to continue.

Click the “PC Software” Icon to install Smart modem software to the specified destination directory.

Select “Program Group” or “Continue” button and wait till it finish the installation and check for the message “Smart Modem Setup was completed successfully”. This indicates that the installation is completed. Then click “OK” button.

Observe the Smart Modem Package in program files.

3.2 GSM AT Commands : 1. line settingsA serial link handler is set with the following default values (factory settings):autobaud, 8 bits data, 1 stop bit, no parity, RTS/CTS flow control.Please use the +IPR, +IFC and +ICF commands to change these settings.

2. Command lineCommands always start with AT (which means ATtention) and finish with a <CR> character.

3. Information responses and result codesResponses start and end with <CR><LF>, except for the ATV0 DCE response format) and the ATQ1 (result code suppression) commands.

If command syntax is incorrect, an ERROR string is returned.If command syntax is correct but with some incorrect parameters, the +CME ERROR: <Err> or +CMS ERROR: <SmsErr> strings are returned with different error codes.If the command line has been performed successfully, an OK string is returned.In some cases, such as “AT+CPIN?” or (unsolicited) incoming events, the product does not return the OK string as a response.

In the following examples <CR> and <CR><LF> are intentionally omitted.

General behaviors :

1. SIM Insertion, SIM Removal SIM card Insertion and Removal procedures are supported. There are software functions relying on positive reading of the hardware SIM detect pin. This pin state (open/closed) is permanently monitored. When the SIM detect pin indicates that a card is present in the SIM connector, the product tries to set up a logical SIM session. The logical SIM session will be set up or not depending on whether the detected card is a SIM Card or not. The AT+CPIN? command delivers the following responses:

If the SIM detect pin indicates “absent”, the response to AT+CPIN? Is “+CME ERROR 10” (SIM not inserted).If the SIM detect pin indicates “present”, and the inserted Card is a SIM Card, the response to AT+CPIN? is “+CPIN: xxx” depending on SIM PIN state.If the SIM detect pin indicates “present”, and the inserted Card is not a SIM Card, the response to AT+CPIN? is CME ERROR 10.These last two states are not given immediately due to background initialization. Between the hardware SIM detect pin indicating “present” and the previous results the AT+CPIN? sends “+CME ERROR: 515” (Please wait, init in progress).When the SIM detect pin indicates card absence, and if a SIM Card was previously inserted, an IMSI detach procedure is performed, all user data is removed from the product (Phonebooks, SMS etc.). The product then switches to emergency mode.

2. Background initializationAfter entering the PIN (Personal Identification Number), some SIM user data files are loaded into the product (Phonebooks, SMS status, etc.). Please be aware that it might take some time to read a large phonebook.

The AT+CPIN? command response comes just after the PIN is checked. After this response user data is loaded (in background). This means that some data may not be available just after PIN entry is confirmed by ’OK’.

The reading of phonebooks will then be refused by “+CME ERROR: 515” or “+CMS ERROR:

515” meaning, “Please wait, service is not available, init in progress”. This type of answer may be sent by the product at several points:

when trying to execute another AT command before the previous one is completed (before response),when switching from ADN to FDN (or FDN to ADN) and trying to read the relevant phonebook immediately,when asking for +CPIN? status immediately after SIM insertion and before the product has determined if the inserted card is a valid SIM Card.

Short Messages commands

1. Parameters definition

<da> Destination Address, coded like GSM 03.40 TP-DA<dcs> Data Coding Scheme, coded like in document [5].<dt> Discharge Time in string format :“yy/MM/dd,hh :mm :sszz”(Year [00-99], Month [01-12], Day [01-31], Hour,Minute, Second and Time Zone [quarters of an hour] )<fo> First Octet, coded like SMS-SUBMIT first octet in document [4], default value is17 for SMS-SUBMIT<index> Place of storage in memory.<length> Text mode (+CMGF=1): number of characters PDU mode (+CMGF=0): length ofthe TP data unit in octets<mem1> Memory used to list, read and delete messages (+CMGL, +CMGR and +CMGD).<mem2> Memory used to write and send messages (+CMGW, +CMSS).<mid> CBM Message Identifier.<mr> Message Reference.<oa> Originator Address.<pid> Protocol Identifier.<pdu> For SMS : GSM 04.11 SC address followed by GSM 03.40 TPDU in hexadecimalformat, coded as specified in doc [4] For CBS : GSM 03.41 TPDU in hexadecimalformat<ra> Recipient Address.<sca> Service Center Address<scts> Service Center Time Stamp in string format :“yy/MM/dd,hh :mm :ss zz”(Year/Month/Day, Hour: Min: Seconds Time Zone)<sn> CBM Serial Number<st> Status of a SMS-STATUS-REPORT<stat> Status of message in memory.<tooa> Type-of-Address of <oa>.<tora> Type-of-Address of <ra>.<tosca> Type-of-Address of <sca>.<total1> Number of message locations in <mem1>.<total2> Number of messages locations in <mem2.

<used1> Total number of messages locations in <mem1>.<used2> Total number of messages locations in <mem2.<vp> Validity Period of the short message, default value is 167

2. Select message service +CSMS

2.1 Description :The supported services are originated (SMS-MO) and terminated shortmessage (SMS-MT) + Cell Broadcast Message (SMS-CB) services.2.2 Syntax :2.3 Defined values :<service>0: SMS AT commands are compatible with GSM 07.05 Phase 2 version 4.7.0.1: SMS AT commands are compatible with GSM 07.05 Phase 2 + version

COMMAND POSSIBLE RESPONSEAT+CSMS=0Note: SMS AT command phase 2 version 4.7.0

+CSMS: 1,1,1OK Note: SMS.MO, SMS-MT and SMS-CB supported

AT+CSMS=1Note: SMS AT command phase 2 +

+CSMS: 1,1,1OK Note: SMS.MO, SMS-MT and SMS-CB supported

AT+CSMS?Note: Current values ?

+CSMS: 1,1,1OK Note: GSM 03.40 and 03.41(SMS AT command phase 2 version 4.7.0

AT+CSMS=?Note :possible services

+CSMS: (0,1)OK

3. New Message Acknowledgement +CNMA

3.1 Description :This command allows reception of a new message routed directly to the TE to be acknowledged.In TEXT mode, only positive acknowledgement to the network (RP-ACK) is possible. In PDU mode, either positive (RP-ACK) or negative (RP-ERROR) acknowledgement to the network is possible.

Acknowledge with +CNMA is possible only if the +CSMS parameter is set to 1 (+CSMS=1) when a +CMT or +CDS indication is shown (see +CNMI command). If no acknowledgement is given within the network timeout, an RP-ERROR is sent to the network, the <mt> and <ds> parameters of the +CNMI command are then reset to zero (do not show new message indication).

3.2 Syntax :Command syntax in text mode :AT+CNMA

Command syntax in PDU mode :AT+CNMA [ = <n> [ , <length> [ <CR>PDU is entered <ctrl-Z / ESC> ] ] ]

Note:PDU is entered using <ackpdu> format instead of <pdu> format (e.g.. SMSC address field is not present). Example of acknowledgement of a new message in TEXT mode

Command Possible responsesAT+CMGF=1Note : Set TEXT mode

OKNote : TEXT mode valid

AT+CNMI=2,2,0,0,0Note : <mt>=2

OK

+CMT :”123456”,”98/10/01,12:3000=00”,129,4.32,240,”15379”,129,5<CR><LF>Received messageNote : message received

AT+CNMANote : acknowledge the message received

OKNote : send positive acknowledgement to the network

AT+CNMANote : try to acknowledge again

+CMS ERROR : 340Note : no+CNMA acknowledgement expected

Example of acknowledgement of a new message in PDU mode:

COMMAND POSSIBLE RESPONSEAT+CMGF=0Note : Set PDU mode

OK Note : Set PDU mode+CMT:,2907913366003000F1240B913366920547F30000003003419404800B506215D42ECFE7E17319Note: message received

AT+CNMA=2<length><CR>…Pdu message…<Ctrl-Z/ESC>Note: negative acknowledgement for the message

OK Note: negative acknowledgement to the network (RP-ERROR) with PDU Message(<ackpdu> format)

3.3 Defined values :<n>: Type of acknowledgement in PDU mode0: send RP-ACK without PDU (same as TEXT mode)1: send RP-ACK with optional PDU message

2: send RP-ERROR with optional PDU message<length> length>: Length of the PDU message

4. Preferred Message Storage +CPMS

4.1 Description :This command allows the message storage area to be selected (for reading, writing, etc).

4.2 Syntax :

4.3 Defined values :<mem1>: Memory used to list, read and delete messages. It can be:- “SM” : SMS message storage in SIM (default)- “BM” : CBM message storage (in volatile memory).- “SR” : Status Report message storage (in SIM if the EF-SMR file exists, otherwise in the M E non volatile memory)Note :“SR” ME non volatile memory is cleared when another SIM card is inserted. It is kept, even after a reset, while the same SIM card is used.

<mem2> : Memory used to write and send messages- “SM” : SMS message storage in SIM (default).

If the command is correct, the following message indication is sent:+CPMS: <used1>,<total1>,<used2>,<total2>When <mem1> is selected, all following +CMGL, +CMGR and +CMGDcommands are related to the type of SMS stored in this memory.

5. Preferred Message Format +CMGF5.1 Description :The message formats supported are text mode and PDU mode.In PDU mode, a complete SMS Message including all header information is given as a binary string (in hexadecimal format). Therefore, only the following set of characters is allowed: {‘0’,’1’,’2’,’3’,’4’,’5’,’6’,’7’,’8’,’9’, ‘A’, ‘B’,’C’,’D’,’E’,’F’}. Each pair or characters is converted to a byte (e.g.: ‘41’ is converted to the ASCII character ‘A’, whose ASCII code is 0x41 or 65).In Text mode, all commands and responses are in ASCII characters. The format selected is stored in EEPROM by the +CSAS command.

HOW TO RUN THE APPLICATION:Select Start --> Programs --> Smart Modem --> Smart Modem, then the following form is appeared as shown below Login

At the application loading time, checks the modem working conditions.

If the modem is not responding, then it displays, Modem not responding message. Click OK to close the application.

Then checkThe modem is Switched Off.The modem is connected to PC-Comport.

If the PC-Comport is already in open mode, then it displays, Port Already Open message. Click OK to close the application.Then Close the Comport.

If the Simcard is not inserted into Modem, then it displays, Check The Simcard message. Click OK to close the application.Insert the Simcard.

If the modem is working properly Error indicator indicates the Green Signal, other wise it indicates the Red Signal.

At the time of checking modem conditions, if any command Buttons or Menu options are selected from application, then it displays, Please wait Checking Modem Connections… message. Wait for the selection of Command Buttons or Menu options until the Error indicates the Green Signal.How to work with Modem:

The application contains the following facilities:SMSVoice CallData Call

Internet

The Menu ContainsFileConfigurationHelpExit

Configuration:

Select the Configuration option from Main Menu then open the configuration formSet the Comport, Baud Rate and Number of Rings, then Click Config Command Button

At Modem Configuration time, the Config, and Cancel buttons are shown in Disable Mode and status will be shown in the Status Bar. After the Completion of Modem Configuration Config, and Cancel Command Buttons are shown in Enable Mode.

Select the Cancel button to Exit from the Configuration Form.SMS (Short Message Services):

Select the SMS option from File Menu, and then open the SMS Form.Type the Message in Text Box (Data Must be below 150 Characters).Enter the phone number to send the Message.

After sending the Message, a message is displayed Message is Send.Select the Cancel button to Exit from the SMS Form.Voice Call:

Select the Voice Call option from File Menu, and then open the Voice Call Form.Enter the phone number to be call.

After the establishment of connection, if the other end is also received, then message is displayed, Modem is Connected…, then Click the OK Button. If the Disconnect is selected then, Modem disconnects the connection. Select the Cancel button to Exit from the Voice Form.Data Call:

Select the Data Call option from File Menu, open the Data Call Form.Enter the phone number to get connected.

After the establishment of connection, Send/Receive, Disconnect options are in Enable mode.

If Send/Receive is selected then, open the Send/Receive form. We can Send or Receive the data simultaneously.

Select the Cancel button to Exit from the Send/Receive form.

If Disconnect is selected then, it gets disconnected.

Select the Cancel button to Exit from the Data Form.Internet:

Select the Internet option from File Menu, and then open the Internet Form.Internet form contains Initialize, APN, Save, Cancel options.

First select Initialize option then, Modem gets initialized. After the modem initialization message is displayed Modem Initialized. If the modem is not initialized then message is displayed Modem not responding. Again select the Initialize option.

If modem is initialized, select APN option then, it prompts for Simcard Name (like “airtelgprs.com”, ”hutchgprs.com”). If APN address is correct then it connects to Network, message is displayed Connected to Network. If APN address is wrong message is displayed Invalid Simcard Name. Again select the APN option.

Select the Save option to save the initialized commands.

After saving the commands Double Click dialing icon, then it establish the Internet connection.

Select the Cancel button to Exit from the Internet form.