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    What is Serial Communication and How it works? [Explained]

    Contents hide 1 Introduction 2 What is Serial communication? 3 Difference between Serial and Parallel communication 4 Clock Synchronization 5 How Serial communication Works? 5.1 # 1 What is Baud rate? 5.2 # 2 Framing […]

    What is Serial Communication and How it works?

    Embedded Systems By Swaroop Updated On November 25, 2018

    Contents hide

    1 Introduction

    2 What is Serial communication?

    3 Difference between Serial and Parallel communication

    4 Clock Synchronization

    5 How Serial communication Works?

    5.1 # 1 What is Baud rate?

    5.2 # 2 Framing

    5.3 # 3 Synchronization

    5.4 # 4 Error Control

    6 Asynchronous Serial Protocols

    6.1 RS-232 protocol 6.2 RS422 Interface 6.3 RS485 Interface 6.4 1-Wire Protocol

    7 Synchronous Serial Protocols

    7.1 I2C Protocol 7.2 SPI Protocol 7.3 CAN Protocol 7.4 USB 7.5 Microwire 8 Conclusion

    Introduction

    Serial communication is the most widely used approach to transfer information between data processing equipment and peripherals. In general, communication means interchange of information between individuals through written documents, verbal words, audio and video lessons.

    Every device might it be your Personal computer or mobile runs on serial protocol. The protocol is the secure and reliable form of communication having a set of rules addressed by the source host (sender) and destination host (receiver). To have a better insight, I have explained the concept of serial communication.

    In embedded system, Serial communication is the way of exchanging data using different methods in the form of serial digital binary. Some of the well-known interfaces used for the data exchange are RS-232, RS-485, I2C, SPI etc.

    What is Serial communication?

    In serial communication, data is in the form of binary pulses. In other words, we can say Binary One represents a logic HIGH or 5 Volts, and zero represents a logic LOW or 0 Volts. Serial communication can take many forms depending on the type of transmission mode and data transfer. The transmission modes are classified as Simplex, Half Duplex, and Full Duplex. There will be a source (also known as a sender) and destination (also called a receiver) for each transmission mode.

    Transmission Modes – Serial Communication

    The Simplex method is a one-way communication technique. Only one client (either the sender or receiver is active at a time). If a sender transmits, the receiver can only accept. Radio and Television transmission are the examples of simplex mode.

    In Half Duplex mode, both sender and receiver are active but not at a time, i.e. if a sender transmits, the receiver can accept but cannot send and vice versa. A good example is an internet. If a client (laptop) sends a request for a web page, the web server processes the application and sends back the information.

    The Full Duplex mode is widely used communication in the world. Here both sender and receiver can transmit and receive at the same time. An example is your smartphone.

    Beyond the transmission modes, we have to consider the endianness and protocol design of the host computer (sender or receiver). Endianness is the way of storing the data at a particular memory address. Depending on the data alignment endian is classified as

    Little Endian and Big Endian.

    Take this example to understand the concept of endianness. Suppose, we have a 32-bit hexadecimal data ABCD87E2. How is this data stored in memory? To have a clear idea, I have explained the difference between Little Endian and Big Endian.

    Little Endian Vs Big Endian

    Data transfer can happen in two ways. They are serial communication and parallel communication. Serial communication is a technique used to send data bit by bit using a two-wires i.e. transmitter (sender) and receiver.

    For example, I want to send an 8-bit binary data 11001110 from the transmitter to the receiver. But, which bit goes out first? Most Significant Bit – MSB (7th bit) or Least Significant Bit- LSB (0th Bit). We cannot say. Here I am considering LSB is moving first (for little Endian).

    Serial Communication

    From the above diagram, for every clock pulse; the transmitter sends a single bit of data to the receiver.

    Parallel communication moves 8,16, or 32 bits of data at a time. Printers and Xerox machines use parallel communication for faster data transfer.

    RS232 Parallel Communication

    Difference between Serial and Parallel communication

    Serial communication sends only one bit at a time. so, these require fewer I/O (input-output) lines. Hence, occupying less space and more resistant to cross-talk. The main advantage of serial communication is, the cost of the entire embedded system becomes cheap and transmits the information over a long distance. Serial transfer is used in DCE (Data communication Equipment) devices like a modem.

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    MODULE - 7SERIAL COMMUNICATION - Part 1(Basics)(I) Introduction:

    Serial communication is common method of transmitting data between a computer and a peripheral device such as a programmable instrument or even another computer. Serial communication transmits data one bit at a time, sequentially, over a single communication line to a receiver. Serial is also a most popular communication protocol that is used by many devices for instrumentation; numerous GPIB-compatible devices also come with an RS-232 based port. This method is used when data transfer rates are very low or the data must be transferred over long distances and also where the cost of cable and synchronization difficulties make parallel communication impractical. Serial communication is popular because most computers have one or more serial ports, so no extra hardware is needed other than a cable to connect the instrument to the computer or two computers together.

    (II) Serial Vs Parallel:

    Let us now try to have a comparative study on parallel and serial communications to understand the differences and advantages & disadvantages of both in detail.

    We know that parallel ports are typically used to connect a PC to a printer and are rarely used for other connections. A parallel port sends and receives data eight bits at a time over eight separate wires or lines. This allows data to be transferred very quickly. However, the setup looks more bulky because of the number of individual wires it must contain. But, in the case of a serial communication, as stated earlier, a serial port sends and receives data, one bit at a time over one wire. While it takes eight times as long to transfer each byte of data this way, only a few wires are required. Although this is slower than parallel communication, which allows the transmission of an entire byte at once, it is simpler and can be used over longer distances. For example, the IEEE 488 specifications for parallel communication state that the cabling between equipment can be no more than 20 meters total, with no more than 2 meters between any two devices; serial, however, can extend as much as1200meters (with high-quality cable).

    So, at first sight it would seem that a serial link must be inferior to a parallel one, because it can transmit less data on each clock tick. However, it is often the case that, in modern technology, serial links can be clocked considerably faster than parallel links, and achieve a higher data rate.

    Even in shorter distance communications, serial computer buses are becoming more common because of a tipping point where the disadvantages of parallel busses (clock skew, interconnect density) outweigh their advantage of simplicity (no need for serializer and deserializer).

    The serial port on your PC is a full-duplex device meaning that it can send and receive data at the same time. In order to be able to do this, it uses separate lines for transmitting and receiving data.

    From the above discussion we could understand that serial communications have many advantages over parallel one like:

    a) Requires fewer interconnecting cables and hence occupies less space.

    b) "Cross talk" is less of an issue, because there are fewer conductors compared to that of parallel communication cables.

    c) Many IC s and peripheral devices have serial interfaces.

    d) Clock skew between different channels is not an issue.

    e) No need of (SERDES).

    f) Cheaper to implement.

    Clock skew:

    Clock skew is a phenomenon in synchronous circuits in which the clock signal sent from the clock circuit arrives at different components at different times, which can be caused by many things, like: -

    a) Wire-interconnect length,

    b) Temperature variations,

    c) Variation in intermediate devices,

    d) Capacitive coupling,

    e) Material imperfections,

    As the clock rate of a circuit increases, timing becomes more critical and less variation can be tolerated if the circuit is to function properly.

    There are two types of clock skew: Positive skew, which occurs when the clock reaches the receiving register later than it reaches the register sending data to the receiving register and negative skew which just opposite: the receiving register gets the clock earlier than the sending register.

    Two types of violation can be caused by clock skew. One problem is caused when the clock travels more slowly than the path from one register to another - allowing data to penetrate two registers in the same clock pulse, or maybe destroying the integrity of the latched data. This is called a hold violation because the previous data is not held long enough at the destination flip-flop to be properly clocked through. Another problem is caused if the destination flip-flop receives the clock pulse earlier than the source flip-flop - the data signal has that much less time to reach the destination flip-flop before the next clock tick. If it fails to do so, a setup violation occurs, so-called because the new data was not set up and stable before the next clock tick arrived. A hold violation is more serious than a setup violation because it cannot be fixed by increasing the clock period. Positive skew and negative skew cannot negatively impact setup and hold timing constraints respectively

    (III) Asynchronous Vs Synchronous data transmission:

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    Embedded System Serial Communicattion

    Embedded System Serial Communicattion for beginners and professionals with characteristics, designing, processors, microcontrollers, tools, addressing modes, assembly language, interrupts, embedded c programming, led blinking, serial communication, lcd programming, keyboard programming etc.

    Serial Communication Calculation and Programming using 8051 Microcontroller

    Computer transfer data in two different ways:-Serial transfer: In serial transfer, data is transfer to device located many meters away this method is used for long distance data transfer.

    Let's see the block diagram of serial data transfer:

    Parallel transfer: In parallel transfer, data is transferred in 8 or more lines. In this wire conductor is used for transferring data to a device that is only a few feet away.

    Let's see the block diagram of parallel data transfer:

    Serial communication is mostly used for transmitting and receiving the signal. The 8051 microcontroller is consisting of Universal Asynchronous Receiver Transmitter (UART) used for serial communication. The signals are transmitted and received by the Rx and Tx pins of microcontroller.

    The UART take individual bytes of data and sends the individual bits in a sequential manner. The registers are used for collecting and storing the data inside a memory. UART is based on half-duplex protocol. Half-duplex means transferring and receiving the data, but not at the same time.

    Let's see the block diagram representation of showing serial communication between flash memory and 8051 microcontroller:

    Let's see the program for transmitting character 'S' using the serial window at baud rate of 9600:

    Consider the 28800 is the maximum baud rate of the 8051 microcontroller For obtaining the 9600 as the baud rate, the timer value is,

    This baud rate '3' is stored inside a timer.

    #include

    void main() {

    SCON=0x50;      //starting of a serial communication//

    TMOD=0x20;    //selected the timer mode//

    TH1=3;       // load the baud rate//

    TR1=1;      //Timer is ON//

    SBUF='S';  //store the character inside a register//

    while(TI==0);   //check the interrupt register//

    TI=0;

    TR1=0;      //OFF the timer//

    while(1);  //continuous loop//

    }

    Let's see the program for receiving the data from the HyperTerminal and sending of that data to PORT 0 of the microcontroller at 9600 baud rate:

    Consider the 28800 is the maximum baud rate of the 8051 microcontroller For obtaining the 9600 as the baud rate, the timer value is,

    This baud rate '3' is stored inside a timer.

    #include

    void main() {

    SCON=0x50;      //starting of a serial communication//

    TMOD=0x20;  //selection of a timer mode//

    TH1=3;       // load the baud rate//

    TR1=1;      //Timer is ON//

    PORT0=SBUF;  //send the data from SBUF to port0//

    while(RI==0);        //checking of an interrupt register//

    RI=0;

    TR1=0;       //OFF the timer//

    while(1); //stop the program when character is received//

    } ← Prev Next →

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