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

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

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