Serial Communication With Arduino

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)

• 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
• in modern PCs one stop bit is standard
• when transferring a text file of ASCII characters using 1 stop bit there is total of 10 bits for each character
• 8 bits for the ASCII code (1 parity bit), 1 bit each for the start and stop bits · for each 8-bit character there are an extra 2 bits, which gives 20% overhead ·

Data transfer rate:

• rate of data transfer bps (bits per second)
• widely used terminology for bps is baud rate
• baud and bps rates are not necessarily equal
• baud rate is defined as the number of signal changes per second

• 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 data from the PC is given in above.

C Code of Serial Transmit:

Simulation of receive data from the PC is given in above.

C Code of Serial Receive:

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