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pythonmicrocontroller

What's the use of /256 and %256 in it and how is the address divided into hi and lo bits?

This is a code snippet from lib_robotis and the value n is the angle that we are inputting(to rotate the dimexel motor).

According to the architecture of the chip within the motor, we require to give the lower bit (identified by lo) of the goal position into the address 0x1e and the higher bit (identified by hi) of the goal position into the address 0x1f.

def move_to_encoder(self,n);
    n=min(max(n,0),self.settings['max_encoder'])
    hi,lo=n/256, n%256
    return self.write_address(0x1e, [hi,lo])
Solution

  • n is a number in the range 0 <= n < 256*256. It takes two bytes to express that number since one byte can encode a value from 0 to 255.

    hi,lo=n/256, n%256

    is the same as 

    hi = n / 256
lo = n % 256

    / is the division operator and % is the remainder operator, so the above code says to divide n by 256 and store the quotient in hi and the remainder in lo. Each of hi and lo will be in the range 0 to 255, so they will each fit into one byte. And n == (256 * hi) + lo, so no information has been lost & the motor controller has all the information it needs to perform the desired operation.

    I assume that the code in your post was written for Python 2; it won't work properly on Python 3. You should replace the n / 256 by n // 256 to make the code work on all versions of Python.

    FWIW, there are various better ways to break a number up into high and low bytes. One uses the built-in divmod function:

    hi, lo = divmod(n, 256)