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; |
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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 If requested baud rate is too high then rounding error of |
Parameters |
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Returns |
|
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; |
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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 |
|
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); |
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Description |
This routine sends one byte via the Software UART bus. |
Parameters |
|
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(); |
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Description |
Soft_UART_Read is blocking routine and it can block the program flow. Calling |
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 .
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.
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