handle multibyte (but not straddling' bits)

Author: ladyada

adafruit_register/i2c_bits.py

@@ -48,12 +48,13 @@ def __init__(self, num_bits, register_address, lowest_bit, register_width=1):
         self.bit_mask = 0
         for _ in range(num_bits):
             self.bit_mask = (self.bit_mask << 1) + 1
-        self.bit_mask = self.bit_mask << lowest_bit
-        if self.bit_mask >= (1 << 8):
-            raise ValueError()
+        self.bit_mask = self.bit_mask << (lowest_bit%8)
+        if self.bit_mask >= 0xFF:
+            raise ValueError("Cannot have more bits than fit in a single byte")
+
         self.buffer = bytearray(1 + register_width)
         self.buffer[0] = register_address
-        self.lowest_bit = lowest_bit
+        self.lowest_bit = lowest_bit % 8  # lowest bit within byte
         self.byte = lowest_bit // 8 + 1
 
     def __get__(self, obj, objtype=None):
@@ -69,6 +70,7 @@ def __set__(self, obj, value):
         with obj.i2c_device as i2c:
             i2c.write(self.buffer, end=1, stop=False)
             i2c.readinto(self.buffer, start=1)
+            
             # Set all of our bits to 1.
             self.buffer[self.byte] |= self.bit_mask
             # Set all 0 bits to 0 by anding together.
@@ -88,4 +90,4 @@ class ROBits(RWBits):
     :param int register_width: The number of bytes in the register. Defaults to 1.
     """
     def __set__(self, obj, value):
-        raise AttributeError()
+        raise AttributeError()