I want to add an cmps03 [ http://www.robot-electronics.co.uk/htm/cmps3tech.htm -- doc] and i dont know with what to start, in pic16f877 it's look simple and easy.  
 
Ideally I would if someone explains me how to implement it on the black-fin like an function for firmware , I have an  C code          [ http://www.robot-electronics.co.uk/files/cmps03_lcd03.c ] shows how to initialize the compass and how to read, if someone could help me with an idea or something more than I'm very much obliged. Thank you.
 
[ code ]
unsigned int get_cmps03(void)
{
unsigned int bearing;
 
     SEN = 1;                                                            // send start bit
     while(SEN);                                                      // and wait for it to clear
     ACKDT = 0;                                                      // acknowledge bit
     SSPIF = 0;
     SSPBUF = CMPS03_ADDR;                              // cmps03 I2C address
     while(!SSPIF);                                                // wait for interrupt
     SSPIF = 0;                                                      // then clear it.
     SSPBUF = 2;                                                      // address of register to read from - high byte of result  
     while(!SSPIF);                                                //  
     SSPIF = 0;                                                      //
     RSEN = 1;                                                      // send repeated start bit
     while(RSEN);                                                // and wait for it to clear
     SSPIF = 0;                                                      //
     SSPBUF = CMPS03_ADDR+1;                              // cmps03 I2C address - with read bit set
     while(!SSPIF);                                                // wait for interrupt
     SSPIF = 0;                                                      // then clear it.
     RCEN = 1;                                                      // start receiving
     while(!STAT_BF);                                          // wait for high byte of bearing
     bearing = SSPBUF<<8;                                    // and get it
     ACKEN = 1;                                                      // start acknowledge sequence
     while(ACKEN);                                                // wait for ack. sequence to end
     RCEN = 1;                                                      // start receiving
     while(!STAT_BF);                                          // wait for low byte of bearing
     bearing += SSPBUF;                                    // and get it
     ACKDT = 1;                                                      // not acknowledge for last byte
     ACKEN = 1;                                                      // start acknowledge sequence
     while(ACKEN);                                                // wait for ack. sequence to end
     PEN = 1;                                                            // send stop bit
     while(PEN);                                                      //
     return bearing;
}

I look into srv firmware and i dont found a function for PWM, it's implemented?  an function Like
  int iPwm(....)//like timer, interval...
{
  
...
return number_count by PWM;
}
 
 
???

Can some one help me with  an example about how i must read this encoders?
I can't understand?I will anyway I read something about it.  
 
Thanks.

Thanks I will try that in this morning, but i have an max3232-se (3.0V <->5V)  and i thing to use it with a few diodes for sense, it's a possibility to work.

The timer only counts to 121000000 and then wraps around.  Because the counter is running at 121MHz, this happens about once per second.  

You can use the encoders() function in picoC to figure out the compass direction and then add some code to use the motors() command turn the robot until the target heading is found.
 
Though it's using a different compass and motor controller, you can see an example of picoC code that turns the robot to a desired heading here -  
    http://code.google.com/p/surveyor-srv1-firmware/source/browse/trunk/blackfin/srv /test4wd.c

The existing encoder function is connected to pins 31 and 32 (GPIO H14 and H15)

There are 2 channels supported by the encoders() function on pins 31 32.  You only need to use one of the channels