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Interview Questions – UART

“In an interview, questions are the bridges between a candidate’s experiences and an employer’s expectations. They pave the way for understanding, insight, and the journey towards finding the perfect professional match. Before entering into UART interview questions, it is suggested to go through the UART protocol tutorial at least once. UART, or Universal Asynchronous Receiver-Transmitter, is a communication protocol used for serial communication between devices. It involves the transmission of data between devices bit by bit, without a shared clock signal.

UART

UART is commonly employed in various applications, serving functions such as connecting microcontrollers to other peripherals, facilitating communication between embedded systems, and interfacing with sensors and other hardware components. Moreover, its versatility extends across a spectrum of use cases. Additionally, this adaptability positions UART as an integral component in diverse fields, showcasing its significance in fostering seamless communication within a wide range of electronic systems

The protocol defines the format of the data being sent, including start and stop bits, data bits, and optional parity for error checking. Additionally, UART provides a simple and versatile method for devices to exchange information serially. Moreover, this inherent flexibility and ease of implementation make it a widely adopted communication standard in various applications, ranging from microcontroller communication to data logging and industrial automation.

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Embedded Protocol – XMODEM

Ward Christensen developed XMODEM, a straightforward file transfer protocol, in 1977. It frequently finds application between two computers employing the XMODEM protocol. The protocol initiates transmission with the ‘C’ character, followed by packets. The receiver provides proper acknowledgment (ACK) for each packet. Identification of the last packet is facilitated by EOT, and the completion of transmission is signaled by ETB.

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8051 Protocol – UART Bit Banging Method

The “8051 Protocol UART Bit Banging Method” is a technique used to implement UART communication on 8051 microcontrollers without relying solely on dedicated hardware UART modules.

Instead, it involves manually toggling GPIO (General Purpose Input/Output) pins to transmit and receive serial data in accordance with the UART protocol. This approach provides flexibility and enables the implementation of UART communication on microcontrollers lacking dedicated UART hardware.

Uses

ApplicationDescription
Low-Cost ProjectsCost-effective solution for implementing UART communication without additional hardware components.
Prototyping and DevelopmentFacilitates quick implementation of UART functionality during the prototyping and development phase, enabling rapid iteration and testing.
Embedded SystemsProvides a compact and resource-efficient solution for adding UART communication capabilities to 8051-based devices in space-constrained environments.
Education and LearningOffers hands-on experience with microcontroller programming and UART implementation, suitable for educational settings to teach serial communication protocols.
Custom Communication ProtocolsEnables the implementation of custom or non-standard communication protocols tailored to specific project requirements, providing flexibility and customization options.
Legacy Systems IntegrationAllows integration with modern communication interfaces and protocols for legacy systems using 8051 microcontrollers lacking dedicated UART hardware support.

Advantages

  • Cost-effective solution, especially for projects with budget constraints.
  • Enables quick implementation of UART functionality during prototyping and development phases, facilitating rapid iteration.
  • Offers versatility and adaptability, suitable for various applications and scenarios.
  • Provides hands-on learning experience with microcontroller programming and UART implementation in educational settings.
  • Allows integration with modern communication interfaces and protocols for legacy systems using 8051 microcontrollers lacking dedicated UART hardware support.

Disadvantages

  • Requires precise timing control for reliable operation, which may be challenging to achieve, especially at higher baud rates.
  • Less efficient compared to hardware-based UART solutions, resulting in potentially slower communication speeds and increased CPU utilization.
  • Consumes more CPU resources and may limit the microcontroller’s ability to perform other tasks concurrently, especially in multitasking applications.
  • Developers with limited experience in low-level hardware interaction may encounter higher implementation complexity when compared to using dedicated hardware UART modules.

Code

code of 8051 Protocol UART Bit Banging Method

#define crystal_freq 11.0592
#include <reg51.h>
#include <intrins.h>

#define uart_ch1 0
#define uart_ch2 2

sbit tx = P2^0;
sbit rx = P2^1;

void delay() {
    int i;
    for(i = 6; i; i--);
    _nop_();
    _nop_();
}

void delay_ms(int i) {
    int j;
    for(; i; i--)
        for(j = 122; j; j--);
}

void tx_data(char data_, char val) {
    char i;
    P2 |= 0x03;
    tx = 0; // send start bit
    P2 &= ~(1 << val);
    delay();

    for(i = 0; i < 8; i++) {
        if(((data_ >> i) & (0x01)) == 0x01) {
            P2 |= (1 << val);
        } else {
            P2 &= ~(1 << val);
        }
        delay();
    }

    P2 |= (1 << val);
    delay();

    // delay_ms(1);
}

void init_uart() {
    tx = 1;
}

void str(char *ch, char uart0_tx) {
    while(*ch) {
        tx_data(*ch++, uart0_tx);
    }
}

void init() {
    SCON = 0x50;
    TMOD = 0x20;
    TH1 = TL1 = 253;
    TR1 = 1;
}

void tx1(char ch) {
    SBUF = ch;
    while(!TI);
    TI = 0;
}

void str1(char *ch) {
    while(*ch) {
        tx1(*ch++);
    }
}

void main() {
    init_uart(); 
    init();
    while(1) {
        str(".........P2^0 IO PIN UART....\n\r", uart_ch1);
        str(".........P2^1 IO PIN UART.....\n\r", uart_ch2);
        str1(".........INBUILT UART ....\n\r");
    }
}

The explanation for 8051 Protocol UART Bit Banging Method Code

#define crystal_freq 11.0592
#include <reg51.h>
#include <intrins.h>

#define uart_ch1 0
#define uart_ch2 2

sbit tx = P2^0;
sbit rx = P2^1;
  • Header Files: The code begins by including necessary header files. reg51.h is specific to the 8051 microcontroller, while intrins.h provides intrinsic functions.
  • Constants: The crystal frequency is defined as 11.0592 MHz. uart_ch1 and uart_ch2 represent UART channels 0 and 2, respectively.
  • Global Variables: Two SFR (Special Function Register) bits tx and rx are declared to represent the transmit and receive pins of the UART.
void delay() {
    int i;
    for(i = 6; i; i--);
    _nop_();
    _nop_();
}

void delay_ms(int i) {
    int j;
    for(; i; i--)
        for(j = 122; j; j--);
}
  • Delay Functions: delay() and delay_ms() are defined to create timing delays. delay() produces a small delay, and delay_ms() generates a delay in milliseconds.
void tx_data(char data_, char val) {
    char i;
    P2 |= 0x03;
    tx = 0; // send start bit
    P2 &= ~(1 << val);
    delay();

    for(i = 0; i < 8; i++) {
        if(((data_ >> i) & (0x01)) == 0x01) {
            P2 |= (1 << val);
        } else {
            P2 &= ~(1 << val);
        }
        delay();
    }

    P2 |= (1 << val);
    delay();

    // delay_ms(1);
}
  • UART Functions: tx_data() is defined to transmit a byte of data (data_) using the specified UART channel (val). It sends start and stop bits and transmits each data bit, waiting for appropriate delays between each bit.
void init_uart() {
    tx = 1;
}
  • UART Initialization: init_uart() initializes the UART communication by setting the transmit pin (tx) to logic high.
void str(char *ch, char uart0_tx) {
    while(*ch) {
        tx_data(*ch++, uart0_tx);
    }
}

void str1(char *ch) {
    while(*ch) {
        tx1(*ch++);
    }
}
  • String Transmission Functions: str() and str1() transmit strings over UART channels 0 and the inbuilt UART, respectively. They iterate over each character in the string and transmit it using the appropriate function (tx_data() or tx1()).
void init() {
    SCON = 0x50;
    TMOD = 0x20;
    TH1 = TL1 = 253;
    TR1 = 1;
}
  • Initialization: init() initializes the UART and timer modes. It sets the serial control register (SCON), timer mode register (TMOD), and timer 1 high and low bytes (TH1 and TL1). Finally, it starts timer 1 (TR1).
void main() {
    init_uart(); 
    init();
    while(1) {
        str(".........P2^0 IO PIN UART....\n\r", uart_ch1);
        str(".........P2^1 IO PIN UART.....\n\r", uart_ch2);
        str1(".........INBUILT UART ....\n\r");
    }
}
  • Main Function: The program’s entry point is the main() function. It first initializes UART communication and timer modes.

Need of Bit Banging

ReasonDescription
Hardware LimitationsIn scenarios where dedicated hardware modules for certain functionalities like UART communication are not available due to cost constraints or limited chip resources, bit banging offers a software-based alternative for implementing these functionalities.
FlexibilityBit banging provides flexibility in implementing custom communication protocols or interfaces that may not be supported by hardware peripherals. This allows developers to tailor the implementation to specific project requirements and integrate with various systems.
Legacy SystemsIn legacy systems or devices using older microcontrollers, hardware support for modern communication protocols may be lacking. Bit banging enables integration with modern communication interfaces without requiring hardware upgrades, extending the lifespan of existing systems.
Educational PurposesBit banging is frequently utilized in education to offer students practical experience with low-level hardware interaction and communication protocols, aiding in their comprehension of digital communication principles.
Debugging and TestingBit banging aids in debugging and testing by enabling manual control of communication signals, facilitating issue diagnosis and system functionality verification, particularly in the absence of hardware-based debugging tools.

NEXT

8051 – Introduction
8051 – Program Methods
8051 – Flash HEX into 8051
8051 – USB ISP Programmer
8051 – Simulators
8051 Interface
8051 Interface – LED
8051 Interface – LCD
8051 Interface – 7 Segment
8051 Interface – Keypad
8051 Interface – Servo
8051 Protocol Interface
8051 – UART Bit banking
8051 – I2C Bit banking (Add Soon)
8051 Tutorials
8051 – 10Khz Square Wave
Others
8051 – Interview Questions

Arduino Interface – UART(Serial)

This tutorial is “Arduino Interface UART(Serial)”. The Universal Asynchronous Receiver-Transmitter (UART) is a fundamental component in microcontroller communication, enabling data exchange between devices. In the realm of Arduino, mastering UART opens doors to interfacing with a plethora of sensors, actuators, and other devices.

Read more: Arduino Interface – UART(Serial)

In this guide, we’ll delve into the basics of UART communication with Arduino. Whether you’re a hobbyist embarking on your first Arduino project or an experienced developer seeking a refresher, this tutorial aims to demystify UART and equip you with the knowledge to integrate it seamlessly into your projects.

Let’s embark on this journey to unravel the intricacies of UART communication with Arduino, from understanding the principles behind UART to implementing it in your own circuits and code.

Use cases

The Arduino UART (Serial) interface offers a wide range of uses across various projects and applications.

ApplicationDescription
Sensor IntegrationInterface with various sensors like temperature sensors, IMUs, GPS modules for data collection.
Wireless CommunicationEstablish wireless links using Bluetooth, Wi-Fi, or Zigbee modules for remote control & IoT.
Display OutputCommunicate with LCDs, OLEDs to present information in projects like digital clocks, weather stations.
Data LoggingLog data to external storage devices for long-term recording in environmental monitoring, tracking systems.
Human-Machine InterfaceCommunicate with external devices like keypads, RFID readers for user interaction in systems.
Control InterfacesControl motors, relays, servo motors for robotics, automated systems, or interactive installations.
Debugging and Serial CommunicationUse for debugging, real-time monitoring, and data transfer between Arduino and PC.
Interfacing with Other DevicesCommunicate with other microcontrollers like Raspberry Pi, ESP8266, enabling collaborative projects.

Print Hello World in Serial terminal

Code

void setup() 
{
  Serial.begin(9600);
  while (! Serial); // Wait untilSerial is ready - Leonardo
  Serial.println("ArunEworld : Hello World");
}
 
void loop() 
{
 
}
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Embedded Protocol – UART

UART (Universal Asynchronous Receiver/Transmitter) is a standard communication protocol used for serial communication between devices. It’s commonly employed in embedded systems for communication between microcontrollers, sensors, and other peripheral devices.

In the context of embedded systems, UART is often used as a hardware communication protocol, enabling devices to transmit and receive data serially. The UART communication involves two pins: TX (transmit) and RX (receive).

  • It’s is full-duplex communication
  • UART contains a shift register
  • which is the fundamental method of conversion between serial and parallel forms.

  • Type of Communication: Asynchronous (No clock).
  • Rule: The transmitter and receiver should same baud rate. Data format and transmission speed are configurable.
  • UART Uses serial communication over a computer or peripheral device serial port. (Electronics Devices).
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