The mikroC PRO for AVR 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).

  Important :

• 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

Prototype	unsigned int Man_Receive_Init();
Returns	0 - if initialization and synchronization were successful. 1 - upon unsuccessful synchronization. 255 - upon user abort.
Description	The function configures Receiver pin and performs synchronization procedure in order to retrieve baud rate out of the incoming signal.   Note : In case of multiple persistent errors on reception, the user should call this routine once again or Man_Synchro routine to enable synchronization.
Requires	Global variables : MANRXPIN : Receive line MANRXPIN_Direction : Direction of the receive pin must be defined before using this function.
Example	// Initialize Receiver sbit MANRXPIN at PORTB0_bit; sbit MANRXPIN_Direction at DDB0_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 PORTB1_bit;
sbit MANTXPIN_Direction at DDB1_bit;
...
Man_Send_Init();

Man_Send

Prototype	void Man_Send(unsigned char tr_data);
Returns	Nothing.
Description	Sends one byte. Parameters : tr_data: data to be sent   Note : Baud rate used is 500 bps.
Requires	To use this function, the user must prepare the MCU for sending. See Man_Send_Init.
Example	unsigned char msg; ... Man_Send(msg);

Man_Synchro

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

Man_Break

Prototype	void Man_Break();
Returns	Nothing.
Description	Man_Receive is blocking routine and it can block the program flow. Call this routine from interrupt to unblock the program execution. This mechanism is similar to WDT.   Note : Interrupts should be disabled before using Manchester routines again (see note at the top of this page).
Requires	Nothing.
Example	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() { TOIE0_bit = 1; // Timer0 overflow interrupt enable TCCR0_bit = 5; // Start timer with 1024 prescaler SREG_I_bit = 0; // Interrupt disable ... Man_Receive_Init(); ... // try Man_Receive with blocking prevention mechanism SREG_I_bit = 1; // Interrupt enable data1 = Man_Receive(&error); SREG_I_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:

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// LCD module connections
sbit LCD_RS at PORTD2_bit;
sbit LCD_EN at PORTD3_bit;
sbit LCD_D4 at PORTD4_bit;
sbit LCD_D5 at PORTD5_bit;
sbit LCD_D6 at PORTD6_bit;
sbit LCD_D7 at PORTD7_bit;

sbit LCD_RS_Direction at DDD2_bit;
sbit LCD_EN_Direction at DDD3_bit;
sbit LCD_D4_Direction at DDD4_bit;
sbit LCD_D5_Direction at DDD5_bit;
sbit LCD_D6_Direction at DDD6_bit;
sbit LCD_D7_Direction at DDD7_bit;
// End LCD module connections

// Manchester module connections
sbit MANRXPIN at PINB0_bit;
sbit MANRXPIN_Direction at DDB0_bit;
sbit MANTXPIN at PORTB1_bit;
sbit MANTXPIN_Direction at DDB1_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:

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// Manchester module connections
sbit MANRXPIN at PINB0_bit;
sbit MANRXPIN_Direction at DDB0_bit;
sbit MANTXPIN at PORTB1_bit;
sbit MANTXPIN_Direction at DDB1_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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