gray code

A binary sequence used to convert the angular position of a disk to digital form. Gray code has the property that only one bit changes between any two positions. A radial line of sensors reads the code off the surface of the disk and if the disk is half-way between two positions each sensor might read its bit from both positions at once but since only one bit differs between the two, the value read is guaranteed to be one of the two valid values rather than some third (invalid) combination (a glitch).

One possible algorithm for generating a gray code sequence is to toggle bits in the order 0, 1, 0, 2, 0, 1, 0, 3, ... This can also be stated as "toggle the lowest numbered bit that results in a new code". Here is a four bit gray code sequence generated in this way:

	0 0 0 0
 	0 0 0 1
 	0 0 1 1
 	0 0 1 0
 	0 1 1 0
 	0 1 1 1
 	0 1 0 1
 	0 1 0 0
 	1 1 0 0
 	1 1 0 1
 	1 1 1 1
 	1 1 1 0
 	1 0 1 0
 	1 0 1 1
 	1 0 0 1
 	1 0 0 0