Software UART Library

The mikroC PRO for PIC provides routines for implementing Software UART communication. These routines are hardware independent and can be used with any MCU.
The Software UART Library provides easy communication with other devices via the RS232 protocol.

Important : The Software UART library implements time-based activities, so interrupts need to be disabled when using it.

Soft_UART_Init

Prototype	char Soft_UART_Init(char port, char* rx_pin, char tx_pin, unsigned long baud_rate, char inverted);
Returns	`2` - error, requested baud rate is too low `1` - error, requested baud rate is too high `0` - successful initialization
Description	Configures and initializes the software UART module. Parameters : `port:` port to be used. `rx_pin:` sets rx_pin to be used. `tx_pin:` sets tx_pin to be used. `baud_rate:` baud rate to be set. Maximum baud rate depends on the MCU’s clock and working conditions. `inverted:` inverted output flag. When set to a non-zero value, inverted logic on output is used. Software UART routines use Delay_Cyc routine. If requested baud rate is too low then calculated parameter for calling `Delay_Cyc` exceeds `Delay_Cyc` argument range. If requested baud rate is too high then rounding error of `Delay_Cyc` argument corrupts Software UART timings.
Requires	Nothing.
Example	This will initialize software UART and establish the communication at 14400 bps: char error; ... error = Soft_UART_Init(&PORTC, 7, 6, 14400, 0); // Initialize Soft UART at 14400 bps

Soft_UART_Read

Prototype	char Soft_UART_Read(char * error);
Returns	Byte received via UART.
Description	The function receives a byte via software UART. This is a blocking function call (waits for start bit). Programmer can unblock it by calling Soft_UART_Break routine. Parameters : `error:` Error flag. Error code is returned through this variable. `0` - no error `1` - stop bit error `255` - user abort, Soft_UART_Break called
Requires	Software UART must be initialized before using this function. See the Soft_UART_Init routine.
Example	char data_, error; ... // wait until data is received do data = Soft_UART_Read(&error); while (error); // Now we can work with data: if (data_) {...}

Soft_UART_Write

Prototype	void Soft_UART_Write(char udata);
Returns	Nothing.
Description	This routine sends one byte via the Software UART bus. Parameters : `udata:` data to be sent.
Requires	Software UART must be initialized before using this function. See the Soft_UART_Init routine. Be aware that during transmission, software UART is incapable of receiving data – data transfer protocol must be set in such a way to prevent loss of information.
Example	char some_byte = 0x0A; ... // Write a byte via Soft UART Soft_UART_Write(some_byte);

Soft_UART_Break

Prototype	void Soft_UART_Break();
Returns	Nothing.
Description	Soft_UART_Read is blocking routine and it can block the program flow. Calling this routine from the interrupt will unblock the program execution. This mechanism is similar to WDT. Note : Interrupts should be disabled before using Software UART routines again (see note at the top of this page).
Requires	Nothing.
Example	char data1, error, counter = 0; void interrupt() { if (INTCON.T0IF) { if (counter >= 20) { Soft_UART_Break(); counter = 0; // reset counter } else counter++; // increment counter INTCON.T0IF = 0; // Clear Timer0 overflow interrupt flag } } void main() { OPTION_REG = 0x04; // TMR0 prescaler set to 1:32 ... if (Soft_UART_Init(&PORTC, 7, 6, 9600, 0) == 0) Soft_UART_Write(0x55); ... // try Soft_UART_Read with blocking prevention mechanism INTCON.GIE = 1; // Global interrupt enable INTCON.T0IE = 1; // Enable Timer0 overflow interrupt data1 = Soft_UART_Read(&error); INTCON.GIE = 0; // Global interrupt disable }

Library Example

This example demonstrates simple data exchange via software UART. If MCU is connected to the PC, you can test the example from the mikroC PRO for PIC USART Terminal Tool.

Copy Code To Clipboard

char i, error, byte_read;                 // Auxiliary variables

void main(){

  ANSEL  = 0;                             // Configure AN pins as digital I/O
  ANSELH = 0;
  
  TRISB = 0x00;                           // Set PORTB as output (error signalization)
  PORTB = 0;                              // No error

  error = Soft_UART_Init(&PORTC, 7, 6, 14400, 0); // Initialize Soft UART at 14400 bps
  if (error > 0) {
    PORTB = error;                        // Signalize Init error
    while(1) ;                            // Stop program
  }
  Delay_ms(100);

  for (i = 'z'; i >= 'A'; i--) {          // Send bytes from 'z' downto 'A'
    Soft_UART_Write(i);
    Delay_ms(100);
  }
   
  while(1) {                              // Endless loop
    byte_read = Soft_UART_Read(&error);   // Read byte, then test error flag
    if (error)                            // If error was detected
      PORTB = error;                      //   signal it on PORTB
    else
      Soft_UART_Write(byte_read);         // If error was not detected, return byte read
    }      
}

Want more examples and libraries?
Find them on