Microcontroller part 7_v1

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Embedded System

PART 7 (UART)ENG.KEROLES SHENOUDA

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Main Concepts

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Embedded communication 3

Physical layerNetworks

Infrared (IR)

Radio frequency (RF)

I2C USB

FireWire

Serial communication

SPIUART

Time Triggered Protocol (TTP)

Local Interconnect Network (LIN)

Media Oriented System Transport (MOST)

Controller Area Network (CAN)

Automotive protocols

TCP/IP (Ethernet Module)

Wireless protocols

Bluetooth

Infrared Data Association (IrDA)

IEEE 802.11

FlexRay










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Simplex, Half-duplex, Full-duplex4










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Serial Vs Parallel 5










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Synchronous Communication6










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Asynchronous Communication7










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Asynchronous8










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Synchronous VS Asynchronous 9










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Single ended vs differential10










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TX/RX relation11

Single MasterSingle Slave

Single MasterMulti Slave Multi Master

Multi Slave










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Bit Rate vs. Baud Rate

Bit Rate: how many data bits are transmitted per second?

Baud Rate: how many symbols are transmitted per second?

These may be different

Extra symbols (channel changes) may be inserted for framing, error detection, acknowledgment, etc. These reduce the bit rate

A single symbol might encode more than one bit. This increases the bit rate.

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UART “Universal asynchronous receiver-transmitter”

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UART - Universal Asynchronous serial Receiver and

Transmitter

Full Duplex mode.(two wires)Asynchronous == No Clock Peer to peer Used to:

Make a communication channel between our micro-controller and our computer

talk to some sensors/chips, the most used ones are serial backpacks for lcd’sand graphical lcd’s and GPS modules that use almost always an serial interface.

The serial protocol is a fairly old protocol created many years ago it was used by terminals

It is Most used with Embedded Linux to show the Linux Kernel log until the login by the UART

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THE UART INTERFACE 15

Compared to I2C, using the UART is darn-easy. UART stands for Universal AsynchronousReceive/Transmit. The hardware can also run in synchronous mode, so it is often called aUSART. A good article about the hardware is at avrbeginners.net. And a good programmingreference is Dean Camera’s UART article at fourwalledcubicle.com.

As opposed to SPI and I2C, which are often used for binary data exchange between hardwaredevices, UART is often used for transmission of (slower) ASCII data. For example, you mightuse the UART for keyboard input or monitor/character LCD output. Speedy SPI transfers datato dedicated hardware devices at MHz speeds, while UART transfers are a thousand timesslower.









http://www.avrbeginners.net/architecture/uart/uart.html

http://www.fourwalledcubicle.com/AVRArticles.php


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Framing the data

Data chunk

The real meat of every serial packet is the data it carries.

The amount of data in each packet can be set to anything from 5 to 9 bits. Certainly, the standard data size is your basic 8-bit byte

Synchronization bits

stop bit(s). these bits mark the beginning and end of a packet. There’s always only one start bit, but the number of stop bits is configurable to either one or two .

The start bit marks the beginning of a new word, When detected, the receiver synchronizes with the new data stream

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Framing the data

Parity bits

The parity bit is added to make the number of 1’s even (even parity) or odd (odd parity)

This bit can be used by the receiver to check for transmission errors

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UART “Asynchronous ” frame 18

Each data frame consists ofa start bit, a variable numberof data bits, an optionalparity bit, and 1 or 2 stopbits. The most commonconfiguration is 1 start bit, 8data bits, no parity bit, and 1stop bit (“8N1”).

In asynchronous mode, there is no clock line: data is transmitted on the transmit line (Tx) andreceived on the receive line (Rx). The UART is initialized by configuring control registers thatdetermine the baud rate, parity, number of stop bits:










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Why use a UART?

A UART may be used when:

– High speed is not required

– A cheap communication line between two devices is required

Asynchronous serial communication is very cheap

– Requires a transmitter and/or receiver

– Single wire for each direction (plus ground wire)

– Relatively simple hardware

– Asynchronous because the

PC devices such as mice and modems used to often be asynchronous serial devices

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UART frame20










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UART Character Transmission

Assume the data width 7 bit

In the configuration shown, it takes 10 bits to send 7 bits of data

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UART Character Transmission

Assume the data width 7 bit

In the configuration shown, it takes 10 bits to send 7 bits of data

• Send the ASCII letter ‘W’ (1010111)

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UART Character Reception

Receiver uses a timer (counter) to time when it samples.

Transmission rate (i.e., bit width) must be known!

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UART Character Reception 24










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UART Character Reception 25










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UART Character Reception

Receiver also verifies that stop bit is ‘1’

If not, reports “framing error” to host system

New start bit can appear immediately after stop bit

Receiver will resynchronize on each start bit

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embedded_systemSo to keep the receiver Sampling in

middle of bits27










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Baud Rate

Baud Rate is The “symbol rate” of the transmission system

For a UART, baud rate is same as the number of bits

per second (bps)

Each bit is 1/(rate) seconds wide

Example: – 9600 baud 9600 Hz

9600 bits per second (bps)

Each bit is 1/(9600 Hz) ≈ 104.17 µs long

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Data Throughput Example29










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What is the difference between

USART vs UART

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USART Universal Synchronous/Asynchronous Receiver/Transmitter

The first difference between a USART and a UART is the way in which the serial data may be clocked.

A UART generates its data clock internally to the microcontroller and synchronizes that clock with the data stream by using the start bit transition. There is no incoming clock signal that is associated with the data,

so in order to properly receive the data stream the receiver needs to know ahead of time what the baud rate should be.

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A USART, on the other hand, can be set up to run in synchronous mode. In this mode the sending peripheral will generate a clock that the receiving peripheral can recover from the data stream without knowing the baud rate ahead of time. Alternatively, the link will use a completely separate line to carry the clock signal. The use of the external clock allows the data rate of the USART to be much higher than that of a standard UART, reaching up to rates of 4 Mbps.










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Are USARTs and UARTs the same?

Technically the answer is no. A USART generally has more capabilities that a

standard UART and the ability to generate clocked data allows the USART to operate at baud rates well beyond a UART's capabilities.

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UART on Atmega32

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USART - Universal Synchronous and Asynchronous serial Receiver

and Transmitter

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USART

Block

Diagram

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USART

Block

Diagram

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USART Block Diagram37

The clock generation logic consists of synchronization logic for external clock

input used by synchronous slaveoperation, and the baud rate generator. The XCK (transfer clock) pin is only used by synchronous transfer mode.










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The Transmitter consists of a single write buffer, a serial Shift Register, Parity

Generator and control logic for handling different serial frame formats.

The write buffer allows a continuous transfer of data without any delay between frames










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The Receiver is the most complex part of the USART module due to its clock and data recovery

units. The recovery units are used for asynchronous data reception. Inaddition to the recovery

units, the Receiver includes a parity checker, control logic, a Shift Register and a

two level receive buffer (UDR). The Receiver supports the same frame formats as the Transmitter, and can detect Frame Error, Data OverRun and Parity Errors.










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Clock Generation

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embedded_systemClock Generation Logic, Block Diagram 41










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Clock Generation Logic, Block Diagram

42Internal Clock Generation – The Baud Rate Generator

is used for the asynchronous and the synchronous master

modes of operation.










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Equations for Calculating Baud Rate Register Setting43










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Equations for Calculating Baud Rate Register Setting44

Double Speed Operation (U2X)

By reduce the divisor

of the baud rate

divider from 16 to 8,

effectively doubling

the transfer

rate for asynchronous communication










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Examples of Baud Rate Setting45










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Synchronous Mode XCK Timing47










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Frame Formats

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Frame Format 49










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Frame Format50










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USART Initialization51










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Data Transmission52










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Data Reception – The USART Receiver53










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Register Description

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Registers55

In the AVR microcontroller five registers are associated with the USART. They are

UBRR (USART Baud Rate Register)

UDR (USART Data Register)

UCSRA (USART Control and Status Register A)

UCSRB (USART Control and Status Register B)

UCSRC (USART Control and Status Register C)

UBRR (12-bit USART Baud Rate Register)

The USART Baud Rate Register (UBRR) is 12-bit (0-4095) register. This register is used to set baud rate of USART.

UDR (8-bit USART Data Register)

UDR is used to send or receive data.










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UDR – USART I/O Data Register56










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UCSRA – USART Control and

Status Register A57










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embedded_systemUCSRA – USART Control and Status Register A

58Bit No. D7 D6 D5 D4 D3 D2 D1 D0 Register Value

Bit Name RXC TXC UDRE FE DOR PE U2X MPCM In DEC In HEX

Value 0 0 0 0 0 0 0 0 00 00

RXCD7 USART Receive Complete

TXCD6 USART Transmit Complete

0 Receive buffer is empty 0Receive buffer is empty so transmit complete

interrupt is executed

1 There is new data in the receive buffer 1Entire frame in the transmit shift register has

been transmitted

UDRED5 USART Data Register Empty

FED4 Frame Error

0 Wait, do not write to UDR 0 No frame error

1 Tramsmit data buffer is empty 1 Frame error has occurred

DORD3 Data Over Run

PED2 Parity Error

0 No Data Over Run 0 No Paroty Error

1 Data over run is detected 1 Parity Error is detected

U2XD1 Double the USART Transmission Speed

MPCMD0 Multi-processor Communication Mode

0 Single Baud Rate 0 Disable Multi-processor Communication Mode

1 Double Date Transfer rate for Asynchronous Communication 1 Enable Multi-processor Communication Mode

UCSRA (USART Control and Status Register A)










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UCSRB – USART Control and

Status Register B59










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UCSRB – USART Control and Status Register B60

Bit No. D7 D6 D5 D4 D3 D2 D1 D0 Register ValueBit Name RXCIE TXCIE UDRIE RXEN TXEN UCSZ2 RXB8 TXB8 In DEC In HEX

Value 0 0 0 1 1 0 0 0 24 18

RXCIED7 Receive Complete Interrupt Enable

TXCIED6 Transmit Complete Interrupt Enable

0 This Interrupt is disabled 0 This Interrupt is disabled

1 This interrupt is enabled 1 This interrupt is enabled

UDRIED5 Data Register Empty Interrupt Enable

RXEND4 Receive Enable

0 This Interrupt is disabled 0 USART receiver is disabled

1 This interrupt is enabled 1 Enable the USART receiver

TXEND3 Transmit Enable

UCSZ2D2 Character Size

0 USART transmitter is disabled 0This bit combined with the UCSZ1:0 bits in UCSRC

sets the number

1 Enable the USART transmitter 1 of data bits (character size) in a frame.

RXB8D1 Receive data bit 8

TXB8D0 Transmit data bit 8

0This is the ninth data bit of the received character when

using serial0

This is the ninth data bit of the transmitted character

when using

1 frames with nine data bits. 1 serial frames with nine data bits.

UCSRB (USART Control and Status Register B)










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UCSRC – USART Control and

Status Register C 61










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UCSRC – USART Control and

Status Register C 62

Bit No. D7 D6 D5 D4 D3 D2 D1 D0 Register Value

Bit Name URSEL UMSEL UPM1 UPM0 USBS UCSZ1 UCSZ0 UCPOL In DEC In HEX

Value 0 0 0 0 0 1 1 0 06 6

URSEL D7Register Select UBRRH or UCSRC because both have same I/O address

UMSEL D6 USART Mode Select

0 UBRRH Register is Selected 0 Asynchronous operation

1 UCSRC register is selected 1 Synchronous operation

UPM1:0 D5 D4 Parity Mode UCSZ1:0 D2 D1 Character Size

0 0 No Parity 0 0 If UCFZ2=0, Character Size = 5

0 1 Reserved 0 1 If UCFZ2=0, Character Size = 6

1 0 Even Parity 1 0 If UCFZ2=0, Character Size = 7

1 1 Odd Parity 1 1If UCFZ2=0, Character Size = 8 else Character Size = 9

USBS D3 Stop Bit Select UCPOL D0 Clock Polarity

0 Use one stop bit 0 This bit is used for synchronous mode only

1 Use two stop bits 1

UCSRC (USART Control and Status Register C)










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UBRR (USART Baud Rate Register)

For a given crystal frequency, the value loaded into the UBRR decides the baud rate.

The relation between the value loaded into UBBR and the Fosc (frequency of oscillator connected to the XTAL1 and XTAL2 pins) is dictated by the following formula:

𝑩𝒂𝒖𝒅 𝑹𝒂𝒕𝒆 =𝑭𝑶𝑺𝑪

𝟏𝟔(𝑼𝑩𝑹𝑹+𝟏)

Example: 𝑩𝒂𝒖𝒅 𝑹𝒂𝒕𝒆 =𝟕𝟑𝟕𝟐𝟖𝟎𝟎

𝟏𝟔(𝟒𝟕+𝟏)=

𝟕𝟑𝟕𝟐𝟖𝟎𝟎

𝟕𝟔𝟖= 𝟗𝟔𝟎𝟎

To get the X value for different baud rates we can solve the equation as follows: 𝑼𝑩𝑹𝑹 =

𝑭𝑶𝑺𝑪

𝟏𝟔×𝑩𝒂𝒖𝒅 𝑹𝒂𝒕𝒆− 𝟏

Example: 𝑼𝑩𝑹𝑹 =𝟕𝟑𝟕𝟐𝟖𝟎𝟎

𝟏𝟔×𝟗𝟔𝟎𝟎− 𝟏 = 𝟒𝟖 − 𝟏 = 𝟒𝟕

The value of UBRR can be from 0 to 4095.

For U2X = 1Replace 16 with 8










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Different Values of UBRR

Fosc = 1.000000 MHz = 1000000Hz Decimal to Hexadecimal Conversion

Baud Rate (bps)

U2X = 0 U2X = 1 In DEC = 254 FE In HEX

UBRR % Error UBRR % Error

110 567.18 0.03 1135.36 0.03300 207.33 0.16 415.67 0.16 Hexadecimal to Decimal Conversion

1,200 51.08 0.16 103.17 0.16 In HEX = FE 254 In DEC

2,400 25.04 0.17 51.08 0.16

4,800 12.02 0.17 25.04 0.17

9,600 5.51 10.21 12.02 0.17 Value of UBRR = 12

19,200 2.26 12.76 5.51 10.21 For U2X = 0 Baud Rate= 4,807.69

38,400 Out of Range 2.26 12.76 For U2X = 1 Baud Rate= 9,615.38

57,600 Out of Range 1.17 17.01

115,200 Out of Range Out of Range

𝑼𝑩𝑹𝑹 =𝑭𝑶𝑺𝑪

𝟏𝟔 × 𝑩𝒂𝒖𝒅 𝑹𝒂𝒕𝒆− 𝟏

𝑩𝒂𝒖𝒅 𝑹𝒂𝒕𝒆 =𝑭𝑶𝑺𝑪

𝟏𝟔(𝑼𝑩𝑹𝑹 + 𝟏)










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UBRRL/H – USART Baud Rate

Register Low/High65










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embedded_systemSteps to Program the AVR to

Transmit the Data Serially:

1. Enable the USART transmitter through UCSRB

2. Use 8 data bits, asynchronous mode, 1 stop bit and no parity through UCSRC

3. Calculate the value to be loaded in UBRR for a desired baud rate generation

4. Write the character into UDR which is to be transmitted serially

5. Monitor UDRE or TXC bits to check if character has been transmitted. You can also enable interrupts associated with above flags to execute their respective ISRs upon completion of transmission.

6. To transmit next character, go to step 4

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embedded_systemSteps to Program the AVR to

Receive the Data Serially:1. Enable the USART receiver through UCSRB

2. Repeat steps 2 and 3 of transmit program

3. Monitor RXC bit to check if character has been received. You can also enable interrupts associated with above flag to execute its respective ISR upon reception of one complete character.

4. To receive next character, go to step 3

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Lab0:UART Polling

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Lab0:UART Polling

Enable USART Receiver and Transmitter

Mode3: Use 8-bit data

For 1 MHz Crystal and 1200 baud rate

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Lab0:UART Polling70

ASCII codeFor ‘c’










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Lab0:

UART

Polling Solution

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Lab1:UART Interrupt

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Lab1:UART interrupt

Enable USART Receiver and Transmitter

Mode3: Use 8-bit data

For 8 MHz Crystal and 1200 baud rate

Enable receive interrupt

73

𝑼𝑩𝑹𝑹 =𝑭𝑶𝑺𝑪

𝟏𝟔×𝑩𝒂𝒖𝒅 𝑹𝒂𝒕𝒆− 𝟏










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Lab1:UART interrupt74










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Lab1:

UART

InterruptSolution










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What happen if I

changed the Fosc to

be 1 Mhz instead of

8Mhz ?

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All the data will be lost

Why …..?Think in depth










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Lab2:two microcontroller

communicates together

through UART

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embedded_systemLab2:two microcontroller communicates

together through UART

Transmitter will act as a counter,

The count Value will be displayed on the 7-segment and also will be sent to the receiver.

The receiver will receive the Count value

From the transmitter and ten will display it on its 7-segment

Crystal Frequency = 1MHz

For 1200 Baud Rate

Use 8-bit data

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embedded_systemLab2:two microcontroller communicates

together through UART80










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Lab2:two microcontroller communicates together through UART

TX 81










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Lab2:two microcontroller communicates together through UART

RX 82










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How to transfer the data between

AVR and PC using normal

asynchronous mode ?

83










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MAX232 – Level Converter IC

The serial port of computer sends/receives data serially at logic levels between -12 to +12V whereas, microcontroller works at logic levels between 0 to 5V (TTL). So we need a RS-232 to TTL and TTL to RS-232 converter and this is done by using RS-232 Level Converter IC, MAX232 between PC and ATmega32.

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FT232 (UART to USB)85










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USART DriverHTTPS://GITHUB.COM/KEROLES/EMBEDDED_SYSTEM/TREE/MASTER/ATMEGA32_DRIVERS/ATMEGA32_DRIVERS/USART

86









https://github.com/keroles/Embedded_System/tree/master/Atmega32_Drivers/ATMEGA32_Drivers/USART


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embedded_system87USART.h










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Repeat the TX in LAB2 by using the

USART Driver

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References

https://www.newbiehack.com/MicrocontrollersABeginnersGuideIntroductionandInterfacinganLCD.aspx

http://www.slideshare.net/MathivananNatarajan/asynchronous-serial-data-communication-and-standards

https://www.slideshare.net/AnkitSingh13/uart-32550652

the avr microcontroller and embedded. System using assembly and c. Muhammad Ali Mazidi

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https://www.newbiehack.com/MicrocontrollersABeginnersGuideIntroductionandInterfacinganLCD.aspx

http://www.slideshare.net/MathivananNatarajan/asynchronous-serial-data-communication-and-standards

https://www.slideshare.net/AnkitSingh13/uart-32550652


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Engineering

Microcontroller part 7_v1