Software UART Library

mikroBasic PRO for ARM provides library which implements 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	sub function Soft_UART_Init(dim byref port as longword, dim rx, tx as longword, dim baud_rate as longword, dim inverted as word) as byte
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 56000 bps: Stellaris ' Initialize Software UART communication at 56000 bps Soft_UART_Init(GPIO_PORTA, 0, 1, 56000, 0) ' Initialize Soft UART at 56000 bps STM32 ' Initialize Software UART communication at 56000 bps Soft_UART_Init(GPIOA_BASE, 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	sub function Soft_UART_Read(dim byref error as byte) as byte
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	dim data_ as byte error as word ... ' wait until data is received do data_ = Soft_UART_Read(error) loop until (error = 0)
Notes	The Software UART library implements time-based activities, so interrupts need to be disabled when using it.

Soft_UART_Write

Prototype	sub procedure Soft_UART_Write(dim udata as byte)
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	dim some_byte as byte ... some_byte = $0A ' 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	sub procedure 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 mikroBasic PRO for ARM USART communication terminal, launch it from the drop-down menu Tools › USART Terminal or simply click the USART Terminal Icon .

Stellaris

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program Soft_UART

dim error_ as byte
    counter, byte_read as byte           ' Auxiliary variables

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) then
    GPIO_PORTD_DATA = error_               ' Signalize Init error
    while TRUE
      nop                                  ' Stop program
    wend
  end if
  Delay_ms(100)

  for counter = "z" to "A" step-1          ' Send bytes from "z" downto "A"
    Soft_UART_Write(counter)
    Delay_ms(100)
  next counter

  while TRUE                               ' Endless loop
    byte_read = Soft_UART_Read(error_)     ' Read byte, then test error flag
    if (error_ <> 0) then                  ' 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
    end if
  wend
end.

STM32

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program Soft_UART

dim error_ as byte
    counter, byte_read as byte           ' Auxiliary variables

main:
  GPIO_Digital_Output(@GPIOD_BASE, _GPIO_PINMASK_ALL) ' digitalni output
  GPIOD_ODR = 0

  error_ = Soft_UART_Init(GPIOA_BASE, 10, 9, 115200, 0) ' Initialize Soft UART at 56000 bps
  if (error_ > 0) then
    GPIOD_ODR = error_               ' Signalize Init error
    while TRUE
      nop                                  ' Stop program
    wend
  end if
  Delay_ms(100)

  for counter = "z" to "A" step-1          ' Send bytes from "z" downto "A"
    Soft_UART_Write(counter)
    Delay_ms(100)
  next counter

  while TRUE                               ' Endless loop
    byte_read = Soft_UART_Read(error_)     ' Read byte, then test error flag
    if (error_ <> 0) then                  ' 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
    end if
  wend
end.

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