The mikroPascal PRO for 8051 provides a library for handling Manchester coded signals. The Manchester code is a code in which data and clock signals are combined to form a single self-synchronizing data stream; each encoded bit contains a transition at the midpoint of a bit period, the direction of transition determines whether the bit is 0 or 1; the second half is the true bit value and the first half is the complement of the true bit value (as shown in the figure below).

Notes:

• The Manchester receive routines are blocking calls (Man_Receive_Init and Man_Synchro). This means that MCU will wait until the task has been performed (e.g. byte is received, synchronization achieved, etc).
• Manchester code library implements time-based activities, so interrupts need to be disabled when using it.

External dependencies of Manchester Code Library

Library Routines

• Man_Receive_Init
• Man_Receive
• Man_Send_Init
• Man_Send
• Man_Synchro
• Man_Break

The following routines are for the internal use by compiler only:

• Manchester_0
• Manchester_1
• Manchester_Out

Man_Receive_Init

// Initialize Receiver
var MANRXPIN : sbit at P0_0_bit;
...
Man_Receive_Init();

Man_Receive

var data, error : byte
...
data := 0
error := 0
data := Man_Receive(&error);

if (error <> 0) then
  begin 
	// error handling 
  end;

Man_Send_Init

// Initialize Transmitter:
var MANTXPIN : sbit at P1_1_bit;
...
Man_Send_Init();

Man_Send

var msg : byte;
...
Man_Send(msg);

Man_Synchro

var man__half_bit_len : word;
...
man__half_bit_len := Man_Synchro();

Man_Break

var data1, error, counter : byte;

procedure Timer1InterruptHandler(); org IVT_ADDR_ET1;
begin
  counter := 0;
  if (counter >= 20) then
  begin
    Man_Break();
    counter := 0;                // reset counter
  end
  else
    Inc(counter);                  // increment counter
end;

begin 
  TR1_bit := 0;                  // Stop Timer1  
  ET1_bit := 1;                  // Enable Timer1 interrupt
  TH1 := 0x00;                   // Set Timer1 high byte
  TL1 := 0x00;                   // Set Timer1 low byte
  TR1_bit := 1;                  // Run Timer1

  EA_bit := 0;                   // Interrupt disable

  ...

  Man_Receive_Init();

  ...
  
  // try Man_Receive with blocking prevention mechanism
  EA_bit := 1;                   // Interrupt enable
  data1 := Man_Receive(@error);
  EA_bit := 0;                   // Interrupt disable

  ...

end;

Library Example

The following code is code for the Manchester receiver, it shows how to use the Manchester Library for receiving data:

program Manchester_Receiver;

// LCD module connections
var LCD_RS : sbit at P2_0_bit;
var LCD_EN : sbit at P2_1_bit;

var LCD_D4 : sbit at P2_2_bit;
var LCD_D5 : sbit at P2_3_bit;
var LCD_D6 : sbit at P2_4_bit;
var LCD_D7 : sbit at P2_5_bit;
// End LCD module connections

// Manchester module connections
var MANRXPIN : sbit at P0_0_bit;
var MANTXPIN : sbit at P0_1_bit;
// End Manchester module connections

var error, counter, ErrorCount, temp : byte;

  begin
    counter := 0;
    ErrorCount := 0;

    Lcd_Init();                                // Initialize LCD
    Lcd_Cmd(_LCD_CLEAR);                       // Clear LCD display

    Man_Receive_Init();                        // Initialize Receiver

    while TRUE do                              // Endless loop
      begin
        Lcd_Cmd(_LCD_FIRST_ROW);               // Move cursor to the 1st row

        while TRUE do                          // Wait for the "start" byte
          begin
            temp := Man_Receive(error);        // Attempt byte receive
            if (temp = 0x0B) then              // "Start" byte, see Transmitter example
              break;                           // We got the starting sequence
            if (error <> 0) then               // Exit so we do not loop forever
              break;
          end;

        repeat
          begin
            temp := Man_Receive(error);        // Attempt byte receive
            if (error <> 0) then               // If error occured
              begin
                Lcd_Chr_CP('?');               // Write question mark on LCD
                Inc(ErrorCount);               // Update error counter
                if (ErrorCount > 20) then      // In case of multiple errors
                  begin
                    temp := Man_Synchro();     // Try to synchronize again
                    //Man_Receive_Init();      // Alternative, try to Initialize Receiver again
                    ErrorCount := 0;           // Reset error counter
                  end;
              end
            else                               // No error occured
              begin
                if (temp <> 0x0E) then         // If "End" byte was received(see Transmitter example)
                  begin                        // do not write anymore received byte on LCD
                    Lcd_Chr_CP(temp);          // else write character on LCD
                    Inc(counter);              // Counts how many chars have been written on LCD
                    if counter = 25 then       // If there were more then 25 characters
                      begin                    // synchronization is off
                        Lcd_Cmd(_LCD_CLEAR);   // Clear the LCD of garbled communication
                        temp := Man_Synchro(); // Try to synchronize again
                      end;
                  end
                else
                  counter := 0;                // reset counter
              end;
            Delay_ms(25);
          end;
        until ( temp = 0x0E );
      end;                                   // If "End" byte was received exit do loop
  end.

The following code is code for the Manchester transmitter, it shows how to use the Manchester Library for transmitting data:

program Manchester_Transmitter;

// Manchester module connections
var MANRXPIN : sbit at P0_0_bit;
var MANTXPIN : sbit at P0_1_bit;
// End Manchester module connections

var index, character : byte;
    s1 : array[16] of char;

  begin
    s1 := 'mikroElektronika';
    Man_Send_Init();                 // Initialize transmitter

    while TRUE do                    // Endless loop
      begin
        Man_Send(0x0B);              // Send "start" byte
        Delay_ms(100);               // Wait for a while

        character := s1[0];          // Take first char from string
        index := 0;                  // Initialize index variable
        while (character <> 0) do    // String ends with zero
          begin
            Man_Send(character);     // Send character
            Delay_ms(90);            // Wait for a while
            Inc(index);              // Increment index variable
            character := s1[index];  // Take next char from string
          end;
        Man_Send(0x0E);              // Send "end" byte
        Delay_ms(1000);
      end;
  end.

Connection Example

Simple Transmitter connection

Simple Receiver connection

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