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.

Contents

1 Uses
2 Advantages
3 Disadvantages
4 Code
5 The explanation for 8051 Protocol UART Bit Banging Method Code
6 Need of Bit Banging
7 NEXT
- 7.1 Explore more

Uses

Application	Description
Low-Cost Projects	Cost-effective solution for implementing UART communication without additional hardware components.
Prototyping and Development	Facilitates quick implementation of UART functionality during the prototyping and development phase, enabling rapid iteration and testing.
Embedded Systems	Provides a compact and resource-efficient solution for adding UART communication capabilities to 8051-based devices in space-constrained environments.
Education and Learning	Offers hands-on experience with microcontroller programming and UART implementation, suitable for educational settings to teach serial communication protocols.
Custom Communication Protocols	Enables the implementation of custom or non-standard communication protocols tailored to specific project requirements, providing flexibility and customization options.
Legacy Systems Integration	Allows 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

Reason	Description
Hardware Limitations	In 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.
Flexibility	Bit 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 Systems	In 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 Purposes	Bit 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 Testing	Bit 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.