Software UART Library

The mikroC PRO for ARM 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.

Library Routines

Soft_UART_Init

Prototype

char Soft_UART_Init(unsigned long *port, unsigned long rx, unsigned long tx, unsigned long baud_rate, unsigned int inverted);

Description

Configures and initializes the software UART module.

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.

Parameters
  • port: software UART port address
  • rx: receiver pin
  • tx: transmiter pin
  • baud_rate: requested baudrate. Maximum baud rate depends on the MCU’s clock and working conditions
  • inverted: if set to non-zero value, indicates inverted logic on output
Returns
  • 2 - error, requested baud rate is too low
  • 1 - error, requested baud rate is too high
  • 0 - successful initialization
Requires

Nothing.

Example

This will initialize software UART and establish the communication at 9600 bps:

Stellaris

char error;
...
 error = Soft_UART_Init(&GPIO_PORTA, 0, 1, 56000, 0);   // Initialize Soft UART at 56000 bps

STM32

char error;
...
 error = Soft_UART_Init(&GPIOA_ODR, 10, 9, 56000, 0);   // Initialize Soft UART at 56000 bps
Notes

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

Soft_UART_Read

Prototype

char Soft_UART_Read(char *error);

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. Values :
  • 0 - no error
  • 1 - stop bit error
  • 255 - user abort, Soft_UART_Break called
Returns

Byte received via UART.

Requires

Software UART must be initialized before using this function. See the Soft_UART_Init routine.

Example
char data_;
char error;
...
// wait until data is received
do
  data = Soft_UART_Read(&error);
while (error);

// Now we can work with data:
if (data_) {...}
Notes

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

Soft_UART_Write

Prototype

void Soft_UART_Write(char udata);

Description

This routine sends one byte via the Software UART bus.

Parameters
  • udata: data to be sent.
Returns

Nothing.

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);
Notes

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

Soft_UART_Break

Prototype

void Soft_UART_Break();

Description

Soft_UART_Read is blocking routine and it can block the program flow. Calling Soft_UART_Break routine from the interrupt will unblock the program execution. This mechanism is similar to WDT.

Parameters

None.

Returns

Nothing.

Requires Nothing.
Example


          
Notes

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

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 ARM USART communication terminal, launch it from the drop-down menu Tools › USART Terminal or simply click the USART Terminal Icon USART Terminal Icon.

Stellaris

char i, error, byte_read;  // Auxiliary variables

void main(){
  GPIO_Digital_Output(&GPIO_PORTD, _GPIO_PINMASK_ALL); // digitalni output
  GPIO_PORTD_DATA = 0;

  error = Soft_UART_Init(&GPIO_PORTA, 0, 1, 56000, 0); // Initialize Soft UART at 56000 bps
  if (error > 0) {
    GPIO_PORTD_DATA = 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
      GPIO_PORTD_DATA = error;                    //   signal it on GPIO_PORTD
    else
      Soft_UART_Write(byte_read);                 // If error was not detected, return byte read
    }
}

STM32

char i, error, byte_read;  // Auxiliary variables

void main(){

  error = Soft_UART_Init(&GPIOA_ODR, 10, 9, 9600, 0); // Initialize Soft UART at 56000 bps
  if (error > 0) {
    GPIOD_ODR = 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
      GPIOD_ODR = error;                    //   signal it on PORTD
    else
      Soft_UART_Write(byte_read);                 // If error was not detected, return byte read
    }
}
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