24-09-2013, 02:45 PM
Gray Codes
Gray Codes.ppt (Size: 147 KB / Downloads: 23)
History of the Gray Code
Invented by Emile Baudot (1845-1903)
Originally called a “cyclic-permuted” code
Telegraph - 5 bit codes
Bits stored on a code wheel in the receiver
Wheel connected to the printing disk
Matched pattern on wheel and received pattern and then actuated head to print.
Exhibited at Universal Exposition, Paris (1878)
Why Gray Codes?
Single output changes at a time
Asynchronous sampling
Permits asynchronous combinational circuits to operate in fundamental mode
Potential for power savings
Multiphase, multifrequency clock generator
Effects of Errors
Lockup States
None if all states are used
Can’t use all states for one-hot