Serial communication is a fundamental feature in embedded systems, allowing microcontrollers to communicate with other devices such as computers, sensors, and other microcontrollers. In the Arduino environment, the Serial.begin function is commonly used to initialize serial communication. However, in the microchip environment, particularly with PIC microcontrollers, the process differs and requires a more hands-on approach to configure the Universal Synchronous Asynchronous Receiver Transmitter (USART) module.

This article will guide you through the steps to initialize serial communication on a PIC microcontroller using MPLAB X IDE and the XC8 compiler. Understanding how to set up serial communication is crucial for debugging, data logging, and interfacing with various peripherals.

Examples:

1. Setting Up the USART Module:

   To initialize serial communication on a PIC microcontroller, you need to configure the USART module. Below is an example of how to set up the USART for a PIC16F877A microcontroller.

   #include <xc.h>
   
   // Configuration bits
   #pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
   #pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
   #pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
   #pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
   #pragma config LVP = OFF        // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3 is digital I/O, HV on MCLR must be used for programming)
   #pragma config CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
   #pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off)
   #pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
   
   void USART_Init(long baud_rate) {
      // Set the baud rate
      unsigned int x;
      x = (_XTAL_FREQ - baud_rate*64)/(baud_rate*64); // For low baud rates
      if(x > 255) {
          x = (_XTAL_FREQ - baud_rate*16)/(baud_rate*16); // For high baud rates
          BRGH = 1;
      }
      if(x < 256) {
          SPBRG = x; // Set the baud rate generator register
          SYNC = 0; // Asynchronous mode
          SPEN = 1; // Enable serial port pins
          TXEN = 1; // Enable transmission
          CREN = 1; // Enable reception
          TX9 = 0; // 8-bit transmission
          RX9 = 0; // 8-bit reception
      }
   }
   
   void USART_TxChar(char out) {
      while(!TRMT); // Wait until the transmit buffer is empty
      TXREG = out; // Transmit the character
   }
   
   char USART_RxChar() {
      while(!RCIF); // Wait until data is received
      return RCREG; // Return the received character
   }
   
   void main() {
      USART_Init(9600); // Initialize USART with 9600 baud rate
   
      while(1) {
          USART_TxChar('H'); // Transmit 'H'
          __delay_ms(1000); // Wait 1 second
      }
   }

2. Explanation:

   • Configuration Bits: These are set to define the microcontroller's operating parameters, such as oscillator type and watchdog timer settings.
   • USART_Init Function: This function initializes the USART module with the specified baud rate. It calculates the value for the SPBRG register based on the desired baud rate and the system clock frequency (_XTAL_FREQ).
   • USART_TxChar Function: This function transmits a single character via the USART module.
   • USART_RxChar Function: This function receives a single character from the USART module.
   • Main Function: This function initializes the USART module and continuously transmits the character 'H' every second.