Software UART Library

The mikroPascal PRO for dsPIC30/33 and PIC24 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

function Soft_UART_Init(var port: word; rx, tx: word; baud_rate : dword; inverted : word) : 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 9600 bps:

// Initialize Software UART communication on pins RF2(Rx), RF3(Tx), at 14400 bps
Soft_UART_Init(PORTF, 2, 3, 14400, 0);
Notes

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

Soft_UART_Read

Prototype

function Soft_UART_Read(var error : byte) : 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
var data_ : byte;
    error : word;
...
// wait until data is received
repeat
  data_ := Soft_UART_Read(error);
until (error = 0);

// Now we can work with data:
if (data_) then begin  ...  end
Notes

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

Soft_UART_Write

Prototype

procedure Soft_UART_Write(udata : 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
var some_byte : 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

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
var data1, error, counter : byte;

procedure Timer1Int(); org IVT_ADDR_T1INTERRUPT;
begin
  counter := 0;
  if (counter >= 20) then
    begin 
      Soft_UART_Break();
      counter := 0;              // reset counter
    end
  else
    Inc(counter);                  // increment counter

  T1IF_bit := 0;                 // Clear Timer1 overflow interrupt flag
end;

begin

  ...

  if (Soft_UART_Init(PORTF, 2, 3, 14400, 0) = 0)
    Soft_UART_Write(0x55);

  ...

  // try Soft_UART_Read with blocking prevention mechanism
  IPC0   := IPC0 or 0x1000;       // Interrupt priority level = 1 
  T1IE_bit := 1;                 // Enable Timer1 interrupts
  T1CON := 0x8030;               // Timer1 ON, internal clock FCY, prescaler 1:256
  data1 := Soft_UART_Read(&error);
  T1IE_bit := 0;                 // Disable Timer1 interrupts
end.
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 mikroPascal PRO for dsPIC30/33 and PIC24 USART communication terminal, launch it from the drop-down menu Tools › USART Terminal or simply click the USART Terminal Icon USART Terminal Icon.

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program Soft_UART;

var error : byte;
    counter, byte_read : byte;             // Auxiliary variables

begin

  ADPCFG := 0xFFFF;                        // Configure AN pins as digital I/O

  TRISB := 0x00;                           // Set PORTB as output (error signalization)
  PORTB := 0;                              // No error

  error := Soft_UART_Init(PORTF, 2, 3, 14400, 0); // Initialize Soft UART at 14400 bps
  if (error > 0) then
    begin
      PORTB := error;                      // Signalize Init error
      while (TRUE) do nop;                 // Stop program
    end;
  Delay_ms(100);

  for counter := 'z' downto 'A' do         // Send bytes from 'z' downto 'A'
    begin
      Soft_UART_Write(counter);
      Delay_ms(100);
    end;

  while TRUE do                            // Endless loop
    begin
      byte_read := Soft_UART_Read(error);  // Read byte, then test error flag
      if (error <> 0) then                 // If error was detected
        PORTB := error                     //   signal it on PORTB
      else
        Soft_UART_Write(byte_read);        // If error was not detected, return byte read
    end;
end.
Copyright (c) 2002-2012 mikroElektronika. All rights reserved.
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