asi_address

def asi_address(start, length):
    """
    Yields the logical address together with ASi address
    look here: http://www.brix.de/elektrik/sps/asi_s7_cp342.html
    """
    n = 0
    for byte in range(start, start + length):
        for bit in range(4, 8):
            yield ('{}.{}'.format(byte, bit), n)
        n += 1
        for bit in range(0, 4):
            yield ('{}.{}'.format(byte, bit), n)
        n += 1