Mumbai University > COMPS > Sem 3 > Digital Logic Design and Analysis

Marks: 4 M

Year: Dec 2014

Gray Code

Gray code is a non-weighted code and is a special case of unit-distance code.

Uses of Gray Code:

1. a) Consider an application where 3- bit binary code is provide to indicate position of the rating disk with the help of brushes.

   b) When brushes are on the black position, they output a 1. When on the white position, they output a 0.

   c) Now, consider what happen when the brushes are on 111 sector and almost to enter 000 sector.

   d) If one brushes slightly ahead to other, say the 3rd brush, then the position indicated 011 instead of 000 or 111. This, result in 1800 error in the disk position.

   e) Since it is physically impossible to have all the brushes precisely aligned, some error will always be present at the edge of sector.

   f) If we use Gray code to represent disk position then error due to improper brush alignment can be reduced. This is because the gray code assures that only one bit will change at one time the decimal number is incremented.

   So, in 3- bit code, error may occur due to one bit position. Other two bit position of two adjacent sector are always same and hence no possibility of error.

Fig(a): shaft position Encoder

2.

Fig(b):Position indicate Binary and Gray code

Therefore, In 3- bit code probability of error is reduced upto 66%. This is important advantage of Gray code and in 4- bit code is reduced upto 75%.

3.It is also used for asynchronous fifo pointer.

4.Used for high speed decode circuit.

5 When Gray code are used in computers to address program memory , the computer uses less power because fever address line change as the program counter advances.

6.Gray code also play a vital role in error correction.