Software UART for PIC16F84A microcontroller with CCS C compiler

The microcontroller PIC16F84A has no hardware UART module, but we can use software UART to send/receive data to/from the PC via RS232 cable (COM port). This topic shows a simple example for the use of the UART protocol with the PIC16F84A MCU.

Hardware Required:

PIC16F84A microcontroller
8MHz crystal
2 x 22pF ceramic capacitors
10K ohm resistor
MAX232 — datasheet
4 x 10uF polarized capacitor
Female RS232 connector
Breadboard
5V power source
Jumper wires

UART Example for PIC16F84A microcontroller circuit:

To interface the PIC16F84A MCU with the PC we need MAX232 signal level converter as shown in the circuit diagram. There are 2 lines between the PIC16F84A and the MAX232 and also two lines between the MAX232 and the female COM connector. One line for data transmit and the other one for data receive.
The female COM connector is connected to the PC using RS232 cable, this cable has to be male-female because the PC RS232 port type is male.
In this example the PIC16F84A MCU runs with 8MHz crystal oscillator.

UART Example for PIC16F84A microcontroller C code:
The function #use rs232(xmit = PIN_B4, rcv = PIN_B5, baud = 2400) is used to configure the UART protocol. Here software UART is used.
where:
xmit is the transmit pin (RB4)
rcv is the receive pin (RB5)
2400 is the baud rate.
The functions used in the C code are:
printf: sends a string of characters over RS232 transmission pin (TX).
putc: send a character over RS232 transmission pin (TX).
getc(): read character if available.
Complete C code for CCS C compiler is below.

// Software UART example for PIC16F84A.

#include <16F84A.h>
#fuses HS, NOWDT, PUT, NOPROTECT
#use delay(clock = 8000000)
#use fast_io(B)
#use rs232(xmit = PIN_B4, rcv = PIN_B5, baud = 2400)

const char message[] = "***** PIC16F84A microcontroller UART example *****" ;
int8 i = 0, j;
void main(){
  output_drive(PIN_B4);
  delay_ms(2000);                                // Wait 2 seconds
  
  // Print text
  printf("Hello world!");
  
  // Print list of characters
  printf("\n\r");                                // Start new line
  while(message[i] != '\0'){                     // Loop until the end of the string
    putc(message[i]);                            // Write character
    delay_ms(100);                               // Wait 100 ms
    i++;                                         // Increment i
  }
  // Print numbers
  printf("\n\r");                                // Start new line
  for(i = 0; i < 21; i++){
    printf("%u\n\r", i);                         // Print i and start new line
    delay_ms(500);
  }
  
  // Receive and send character via UART
  while(TRUE){
    j = getc();                                // UART read character
    putc(j);                                   // Send it back
  }
}

// Software UART example for PIC16F84A.

#include <16F84A.h>

#fuses HS, NOWDT, PUT, NOPROTECT

#use delay(clock = 8000000)

#use fast_io(B)

#use rs232(xmit = PIN_B4, rcv = PIN_B5, baud = 2400)

const char message[] = "***** PIC16F84A microcontroller UART example *****" ;

int8 i = 0, j;

void main(){

output_drive(PIN_B4);

delay_ms(2000); // Wait 2 seconds

// Print text

printf("Hello world!");

// Print list of characters

printf("\n\r"); // Start new line

while(message[i] != '\0'){ // Loop until the end of the string

putc(message[i]); // Write character

delay_ms(100); // Wait 100 ms

i++; // Increment i

}

// Print numbers

printf("\n\r"); // Start new line

for(i = 0; i < 21; i++){

printf("%u\n\r", i); // Print i and start new line

delay_ms(500);

}

// Receive and send character via UART

while(TRUE){

j = getc(); // UART read character

putc(j); // Send it back

}

Discover more from Simple Circuit

Subscribe to get the latest posts sent to your email.

Discover more from Simple Circuit

Related Posts

Leave a Comment Cancel Reply