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llowing features are required:

Baud rate
Start bits
Data bits
Parity bits
Character Frame

Idle

Space

Mark

Idle

Stop Bits

Parity Bits

Data Bits

Start Bits

Stop bits
Figure 4-1: Character frame encoding

4.4.1Baud Rate

The baud rate of a transmission is how many symbols are transferred in a second. There are two voltage stages MARK and SPACE. MARK represents the negative voltage and SPACE represents the positive voltage.

4.4.2Start Bits

Start bit informs about the initialization of a new frame of data. The duration of start bit is the reciprocal of the baud rate. If Baud rate of the transmission is 9600 then the duration of start bit will be 0.104ms and the entire character frame of 11 bits would be transmitted in 1.146ms.

4.4.3Data Bits

Data bits represent data in a character frame. The order of transmission is from LSB to MSB.

4.4.4Parity Bits

It is an optional bit in the data frame. It is transmitted after the data bits. It helps in error checking and detection of data corruption. There are different ways of parity checking i.e. even parity or odd parity. The number of marks is counted in a data frame and if the number is even a single bit is used to represent that the parity is even similarly if the number of logic 1 is odd a single bit represents that the parity of the data frame is odd. For the case of even parity the bit is 1 and for the case of odd parity the bit is 0.

4.4.5Stop Bits

In a character frame stop bits is the last frame. Stop bits are represented by a negative voltage (SPACE). The stop bit stays at the MARK (negative position) is no further data is transmitted. Otherwise a start bit of SPACE (positive voltage) is transmitted.

4.6AT Commands

AT is the Attention command. This command instructs the modem to perform many communication tasks e.g. dial, answer hook control etc. All the modem commands precedes this attention command except A/ and +++.

AT+CMGF

This command is used to check the mode of operation of the mobile. There are two modes for mobile communication

Text mode
PDU mode (Protocol Data Unit)
AT + CMGF = 1 refers to PDU mode whereas AT+CMGF = 0 refers to text PDU mode.

AT + CMGF =? refers to the mode which is in used after execution.

AT+CMGR

The command reads the message from a desired memory location. E.g. if AT + CMGR = 1 then it will read the message from first memory location.

AT+CMGD

The command deletes the message from a desired memory location .E.g AT+CMGD = 0 deletes the message from index 0.

AT+CPMS

This command is used to read, write, delete, send and receive from memory storage.

AT+CPMS = 'ME' refers to message storage on mobile phone. AT+CPMS = 'SIM” refers to message storage on SIM.

AT+CNMI

The command gives the indication of new message. AT+CNMI = 2,1,2,0,0

AT+CMGS ='Any mobile number'

This command confirms that either switching on or off of device is performed or not. This command sends message to the ph本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。