serial communication protocols

7/29/2019 Serial Communication Protocols

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Serial CommunicationProtocols

Dedicated to New Learners by13-02-13 K.Viswanath


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Mode of Communication Clock Pulse and Its significance.

Asynchronous and synchronous Protocol. UART(RS232/485/422). SPI(Serial Peripheral Interface).

I2C(Inter Integrated Circuit). Methods of SW Implementation. Interfacing with Peripherals

Contenido.


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Mode of Communication


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Clock Pulse and Its significance

In electronics and especially synchronous digital circuits, a ClockSignal is a particular type of signal that oscillates between a highand a low state and is utilized like a metronome.

Metronome is a machine, to coordinate actions of circuits.

Although the word signal has a number of other meanings, theterm here is used for "transmitted energy that can carry

information".

In other words to say which drives other peripherals.


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Application

Mechanical metronome

A metronome is any device thatproduces regular, metrical ticks(beats, clicks) settable in beats

per minute.

These ticks represent a fixed,regular aural pulse.


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Difference Asynchronous and

synchronous

In asynchronous serial transmission, each character is packaged inan envelope, and sent across a single wire, bit by bit to a receiver.Because no signal lines are used to convey clock (timing)information, this method groups data together into a sequence of bits

(5-8), then prefixes them with a start bit and appends the data witha stop bit.This is very flexible but has a lot of overhead.


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In synchronous transmission, envelop the information, but withmore characters between the start and end sequences.The start and stop bits are replaced with a new format thatpermits greater flexibility. An extra ending sequence is added toperform error checking.Receiver and Transmitter are synchronized by a clock signal,either transmitted over a separate wire. More data can be sentafter a short synchronizing sequence.Which achieves Lower

overhead and thus,greater throughput.

Ex: SPI and I2C.

Difference Asynchronous and

synchronous


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UART(RS232/485/422)

A Universal Asynchronous Receiver/Transmitter.UARTs are commonly used in conjunction with communication standards such

as EIA, RS-232, RS-422 or RS-485.The electric signaling levels and methods (such as differential signaling etc.)

are handled by a driver circuit external to the UART.


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Bit Time = 1/Baud Rate

One frame contains 1+8+1 = Start Bit + Data Byte + Stop bit

Character framing
http://en.wikipedia.org/wiki/File:Charactercode.png


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RS232

RS-232(Recommended Standard 232) is a standard for serial binarydata signals connecting between a Data Terminal Equipment (DTE) and aData Communication Equipment (DCE). Significant differences betweenTTL level UART and RS-232 is the voltage level.

Valid signals in RS-232 are 3 to 15V, and signals near 0V is not avalid RS-232 level.Besides voltage level, the RS-232 also has a few extra pins specificallydesigned for the communication between PC and modem. The pinouts ofthe DB-9 and their functions


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RS232 DB9 Connector

Name Pin Description

Transmitted Data

(TxD)

3 Serial data output

Received Data

(RxD)

2 Serial data input

Request to Send

(RTS)

7 This line informs the DCE (Modem)

that the DTE (PC) is ready to

exchange data

Clear to Send(CTS)

8 This line indicates that the DCE isready to exchange data

Data Terminal

Ready (DTR)

4 Asserted by DTE to indicate that it is

ready to be connected

Data Set Ready

(DSR)

6 Asserted by DCE to indicate the DCE

is powered on and is ready to receive

commands or data for transmissionfrom the DTE

Data Carrier

Detect (DCD)

1 Asserted by DCE when a connection

has been established with remote

equipment

Ring Indicator

(RI)

9 Asserted by DCE when it detects a

ring signal from the telephone line


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interfacing microcontroller to PC

serial port


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RS-422 - RS-485

RS-422 (also EIA-422) is a technical standard that specifies electricalcharacteristics of a digital signaling circuit. Differential signaling cantransmit data at rates as high as 10 million bits per second, or may besent on cables as long as 1500 meters. Some systems directlyinterconnect using RS-422 signals, or RS-422 converters may beused to extend the range of RS-232 connections. The standard onlydefines signal levels; other properties of a serial interface are set byother standards

EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining

the electrical characteristics of drivers and receivers for use in balanceddigital multipoint systems. The standard is published bythe Telecommunications Industry Association/Electronic IndustriesAlliance (TIA/EIA). Digital communications networks implementing theEIA-485 standard can be used effectively over long distances and in

electrically noisy environments. Multiple receivers may be connected tosuch a network in a linear multi-dro confi uration. These characteristics


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SPI (Serial Peripheral Interface)
http://en.wikipedia.org/wiki/File:SPI_8-bit_circular_transfer.svg


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http://en.wikipedia.org/wiki/File:SPI_timing_diagram2.svg


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I2C.


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I2C Bus Arbitration:


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Methods of SW Implementation

Polling Method. Interrupt Method. Bit-banging or peripheral in Controller

SW Development Steps:

Configuration.

Reception.

Transmission. Error Status/Acknowledgement.


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SW Development Steps:

Polling Method.

Ex: UART: for Transmission :

while(Transmitter empty flag & UxTCTL){

// source code lines}

For Reception mostly Interrupt method is used

( either peripheral IO or GPIO interrupt for bit banging)

Interrupt Method.

Ex: UART: for Transmission :1. Place the Data into the UART_TxBUFFER_REGISTER

Enable the Interrupt Flag in the UART Interrupt Register.2. Few code lines will be placed in the Tx Interrupt, to check the

end of the data Byte.


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serial communication protocols

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