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    USART Serial Port in AVR Microcontrollers: (Chapter 11 of The Mazidi's Book)

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    Yagnesh
    1. The document discusses serial communication in AVR microcontrollers, focusing on the USART serial port. It describes several serial communication standards used in AVRs including USART, SPI, and I2C. 2. USART provides both synchronous and asynchronous serial communication. It is controlled via registers that specify the communication mode, parity, data length, and transmission rate. 3. Programming the USART in C involves setting values in registers like UCSRA, UCSRB, UCSRC, and UBRR to control the serial port and transmit/receive data via the UDR register.

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    Download as PDF, TXT or read online from Scribd

    USART Serial Port in AVR Microcontrollers: (Chapter 11 of The Mazidi's Book)

    Uploaded by

    Yagnesh
    91 views37 pages
    1. The document discusses serial communication in AVR microcontrollers, focusing on the USART serial port. It describes several serial communication standards used in AVRs including USART, SPI, and I2C. 2. USART provides both synchronous and asynchronous serial communication. It is controlled via registers that specify the communication mode, parity, data length, and transmission rate. 3. Programming the USART in C involves setting values in registers like UCSRA, UCSRB, UCSRC, and UBRR to control the serial port and transmit/receive data via the UDR register.

    Original Description:

    USART registers necessary for the serial communication

    Original Title

    Micro l6 Usart

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    1. The document discusses serial communication in AVR microcontrollers, focusing on the USART serial port. It describes several serial communication standards used in AVRs including USART, SPI, and I2C. 2. USART provides both synchronous and asynchronous serial communication. It is controlled via registers that specify the communication mode, parity, data length, and transmission rate. 3. Programming the USART in C involves setting values in registers like UCSRA, UCSRB, UCSRC, and UBRR to control the serial port and transmit/receive data via the UDR register.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    91 views37 pages

    USART Serial Port in AVR Microcontrollers: (Chapter 11 of The Mazidi's Book)

    Uploaded by

    Yagnesh
    1. The document discusses serial communication in AVR microcontrollers, focusing on the USART serial port. It describes several serial communication standards used in AVRs including USART, SPI, and I2C. 2. USART provides both synchronous and asynchronous serial communication. It is controlled via registers that specify the communication mode, parity, data length, and transmission rate. 3. Programming the USART in C involves setting values in registers like UCSRA, UCSRB, UCSRC, and UBRR to control the serial port and transmit/receive data via the UDR register.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    of 37

    Microprocessors, Lecture 6:

    USART Serial Port in AVR Microcontrollers


    (Chapter 11 of the Mazidis book)

    Contents
    Serial communication
    Serial communication programming in C

    University of Tehran 2

    Serial ports in AVR

    University of Tehran 3

    Serial ports in AVR


    USART: and old and widely used
    standard (pins 14 and 15 of
    ATmega32)
    SPI: very high-speed (~ two
    orders of magnitude faster than
    USART) synchronous serial port
    For example for high-speed
    data transfer to EPROM
    Pins 5,6,and 7 of Atmega32
    I2C (Inter IC)
    Connection using a shared bus
    connecting up to 128 devices
    Pins 22 and 23 of ATmega32
    University of Tehran 4

    Data transmission

    Data transmission between AVR and peripheral


    devices like sensors is straightforward
    Connect the device to one of the AVR ports and read
    the port

    Data transmission between two AVRs or an AVR


    and a PC is more complex
    Requires a communication protocol

    Communication Protocol: a set of standards and


    rules that orchestrates data communication
    between two or more devices

    University of Tehran 5

    RS232

    An old standard for serial communication


    Still used in many devices like PCs
    Is used in serial port (COM port) of PCs

    PCs used to have 2 COM ports, but


    today PCs have one port or no port
    Replaced with USB ports

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    RS232
    Requires 3 pins:
    RXD= receive, TXD: transmit, GND= ground
    The RXD and TXD pins are cross-connected

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    COM ports

    COM = communication port


    Find it at the back of your PC case!
    Pins 2,3,and 5 are TXD,RXD, and GND,
    respectively.

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    Serial communication in AVR


    USART: a standard IC that provides both synchronous and
    asynchronous communication
    A peripheral IC of the AVR microcontrollers
    Connected to RXD and TXD pins of Atmega32

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    USART
    USART: Universal Synchronous/Asynchronous
    Receiver Transmitter
    An standard IC that can provide both
    synchronous and asynchronous communication
    It is controlled by some AVR registers

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    USART block diagram in AVR

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    USART

    The control registers specify:

    The mode of operation: synchronous or asynchronous


    Parity bit: odd or even
    Information unit: 5,6,7,8, or 9 bits
    Information unit separation: how to specify the
    transmission of a word starts and stops?
    Transmission rate
    .

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    Parity bit
    A way to detect error during data transmission
    Due to external noises

    Even parity= the number of 1s must be an even


    number
    Add an extra bit to the 8-bit data, called parity bit
    How does it work?
    if the number of 1s is already even, set it to 0,
    otherwise to 1
    Send the parity bit with data
    If the other side detects odd number of 1s, there is
    something wrong

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    Transmission rate

    Baud rate vs bit rate


    Baud rate: the number signal changes in a second
    Bit rate: the number of bits transmitted per second
    Baud rate is not necessarily equal to bit rate
    Each signal may carry several bits!

    A signal with 8 levels can carry 3 bits

    If baud rate=x, bit rate=3x


    In USART, baud rate= bit rate
    The bit rate of both devices connected to the same
    serial port must be the same

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    AVR serial port programming

    Setting different registers


    5 registers are associated with serial port:
    UDR: USART data register
    UCSRA, UCSRB, UCSRC: USART control and
    status register
    UBRR: USART baud rate register

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    UDR

    USART data register


    Actually two registers: one for the transmit
    direction, the other for receive direction
    Share the same address and name
    When UDR is read, the data received from the
    serial line is returned
    When a data is written to UDR, it is directed to
    the transmit line

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    UDR

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    UCSR

    USART control and status register


    Three 8-bit registers to control the USART
    operation

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    UCSRA

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    UCSRA- continue

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    UCSRA- continue

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    UCSRB

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    UCSRB- continue

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    UCSRC

    Note on bit7: UCSRC and UBBR share the


    same address due to some technical issue. Set
    URSEL=1 when you want the data to be written
    to UCSRC, otherwise set URSEL=0 to write to
    UBBR
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    UCSRC- continue

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    UCSR
    Character size of the transmitted and received
    data- is same for both directions

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    UBRR

    USART Baud Rate Register


    12 bits
    The most significant byte has a shared address
    with UCSRC!

    X= UBBR[0-11]
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    USART baud rate

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    Sampling

    Sampling rate: 16 times faster than baud rate


    2 out of 3 majority voting in cycles 8 to 9

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    USART in Tx mode

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    USART in Rx mode

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    Synchronous mode

    Work in master-slave mode


    The master send clock signal to slave

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    Synchronous mode

    UCPOL: bit 7 in UCSRC


    Baud rate= fosc/(2(UBBR+1))
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    USART programming in C
    Send a sequence of numbers started from 0
    every 350ms to TXD pin
    Check RXD pin and if the received number is
    0x55 set PD.6 (bit 6 of port D) to 1
    0x66 set PD.6 to 0

    1 stop bit, no parity, 8 bit, asynchronous

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    Code vision configuration

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    USART programming in C
    main()
    {
    int a=0;
    DDRD.6=1;
    UCSRA=0x0;
    UCSRB=0x98; //10011000 (RXIE=1, RXEN=1, TXEN=1)
    UCSRC=0x86;// 10000110 (URSEL=1,asynch, no parity, one stop bit, 8 bit)
    UBRRH=0;// just set a rate that guarantees the data transfer can be completed before 350ms
    UBRRL=0x08;
    Interrupt [USART_RXC] usart_rx_isr()
    #asm(sei);
    {
    while(1)
    char data;
    {
    data=UDR;
    UDR= a++;
    if(data==0x55)
    delay_ms(350);
    PORTD.6=1;
    if(data==0x66)
    }
    PORTD.6=0;
    }
    }
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    USART in PCs

    Implemented by the 8251 IC

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