Serial Communication With 8051

SERIAL COMMUNICATION:

Serial Communication uses single data line making it much cheaperEnables two computers in different cities to communicate over the telephonebyte of data must be converted to serial bits using a parallel-in-serial-out shift register and transmitted over a single data lineReceiving end there must be a serial-in-parallel-out shift registerif transferred on the telephone line, it must be converted to audio tones by modemfor short distance the signal can be transferred using wirehow PC keyboards transfer data to the motherboard2 methods, asynchronous and synchronousSynchronous method transfers a block of data (characters) at a timeAsynchronous method transfers a single byte at a timeUses special IC chips called UART (universal asynchronous receiver-transmitter) and USART (universal synchronous asynchronous receiver-transmitter)

Half- and Full-duplex Transmission

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

Start and stop bits

asynchronous method, each character is placed between start and stop bits · called framing · start bit is always one bitstop 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

RS232 Standards

most widely used serial I/O interfacing standard
input and output voltage levels are not TTL compatible1 bit is represented by -3 to -25 V0 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

Data Communication Classification

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