Serial Communication With AVR Microcontroller

BASICS OF SERIAL COMMUNICATION:

• serial communication uses single data line making it much cheaper ·
• enables two computers in different cities to communicate over the telephone ·
• byte of data must be converted to serial bits using a parallel-in-serial-out shift register and transmitted over a single data line ·
• receiving end there must be a serial-in-parallel-out shift register ·
• if transferred on the telephone line, it must be converted to audio tones by modem ·
• for short distance the signal can be transferred using wire ·
• how PC keyboards transfer data to the motherboard ·
• 2 methods, asynchronous and synchronous ·
• synchronous method transfers a block of data (characters) at a time ·
• asynchronous method transfers a single byte at a time ·
• Uses special IC chips called UART (universal asynchronous receiver-transmitter) and USART (universal synchronous asynchronous receiver-transmitter) ·

• if the data can be transmitted and received, it is a duplex transmission
• simplex transmissions the computer only sends data ·
• duplex transmissions can be half or full duplex ·
• depends on whether or not the data transfer can be simultaneous ·
• If one way at a time, it is half duplex ·
• If can go both ways at the same time, it is full duplex ·
• full duplex requires two wire conductors for the data lines (in addition to the signal ground)

· Asynchronous serial communication and data framing

• ·data coming in 0s and 1s ·
• to make sense of the data sender and receiver agree on a set of rules ·
• Protocol ·
• how the data is packed ·
• how many bits/character ·
• when the data begins and ends ·
• Start and stop bits ·
• asynchronous method, each character is placed between start and stop bits · called framing ·
• start bit is always one bit ·
• stop bit can be one or two bits ·
• start bit is always a 0 (low) ·
• stop bit(s) is 1 (high) ·
• LSB is sent out first

• most widely used serial I/O interfacing standard
• input and output voltage levels are not TTL compatible ·
• 1 bit is represented by -3 to -25 V ·
• 0 bit is +3 to +25 V ·
• -3 to +3 is undefined ·
• to connect RS232 to a microcontroller system must use voltage converters such as MAX232 to convert the TTL logic levels to the RS232 voltage levels, and vice versa ·
• MAX232 IC chips are commonly referred to as line drivers

• DTE (data terminal equipment)
• DCE (data communication equipment) ·
• DTE - terminals and computers that send and receive data ·
• DCE - communication equipment responsible for transferring the data ·
• simplest connection between a PC and microcontroller requires a minimum of three pins, TxD, RxD, and ground

Simulation of transmit " A" is given in above.

C Code of transmit " A " :

Simulation of transmit " Welcome To All " is given in above.

C Code of transmit " Welcome To All " :

Simulation of receive is given in above.

C Code of receive :

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