The mikroC 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
sbit MANRXPIN at P0_0_bit;
...
Man_Receive_Init();

Man_Receive

unsigned char data = 0, error = 0;
...
data = Man_Receive(&error);
if (error)
  { /* error handling */ }

Man_Send_Init

// Initialize Transmitter:
sbit MANTXPIN at P0_1_bit;
...
Man_Send_Init();

Man_Send

unsigned char msg;
...
Man_Send(msg);

Man_Synchro

unsigned int man__half_bit_len;
...
man__half_bit_len = Man_Synchro();

Man_Break

char data1, error, counter = 0;

void Timer0Overflow_ISR() org 0x12 {

  if (counter >= 20) {
    Man_Break();
    counter = 0;                // reset counter
  }
  else
    counter++;                  // increment counter
}

void main() {

  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

  ...
}

Library Example

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

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

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

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

char error, ErrorCount, temp;

void main() {
  ErrorCount = 0;
  Lcd_Init();                                     // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);                            // Clear LCD display

  Man_Receive_Init();                             // Initialize Receiver
  
  while (1) {                                     // Endless loop

      Lcd_Cmd(_LCD_FIRST_ROW);                    // Move cursor to the 1st row
       
      while (1) {                                 // Wait for the "start" byte
        temp = Man_Receive(&error);               // Attempt byte receive 
        if (temp == 0x0B)                         // "Start" byte, see Transmitter example
          break;                                  // We got the starting sequence
        if (error)                                // Exit so we do not loop forever
          break;
        }
        
      do
        {
          temp = Man_Receive(&error);             // Attempt byte receive
          if (error) {                            // If error occured
            Lcd_Chr_CP('?');                      // Write question mark on LCD
            ErrorCount++;                         // Update error counter
            if (ErrorCount > 20) {                // In case of multiple errors
              temp = Man_Synchro();               // Try to synchronize again
              //Man_Receive_Init();               // Alternative, try to Initialize Receiver again
              ErrorCount = 0;                     // Reset error counter
              }
            }
          else {                                  // No error occured
            if (temp != 0x0E)                     // If "End" byte was received(see Transmitter example)
              Lcd_Chr_CP(temp);                   //   do not write received byte on LCD
              }
          Delay_ms(25);
        }
      while (temp != 0x0E) ;                      // If "End" byte was received exit do loop
   }
}

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

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

char index, character;
char s1[] = "mikroElektronika";

void main() {

  Man_Send_Init();                 // Initialize transmitter

  while (1) {                      // Endless loop
    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) {            // String ends with zero
      Man_Send(character);         // Send character
      Delay_ms(90);                // Wait for a while 
      index++;                     // Increment index variable
      character = s1[index];       // Take next char from string 
      }
    Man_Send(0x0E);                // Send "end" byte
    Delay_ms(1000);
  }
}

Connection Example

Simple Transmitter connection

Simple Receiver connection

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