03-05-2012, 11:49 AM
STATE MACHINE ENCODING
STATE MACHINE ENCODING - Copy.pptx (Size: 68.43 KB / Downloads: 33)
State Transition Graph:
Describes state machine in terms of its input and output at that particular state and its transition to the next state.
State Machine Synthesis Process:
It generates a gate-level circuit based on machine’s specifications.
It allocates state register and assigns binary codes to represent symbolic states,this process is called “Encoding”.
Transition Analysis of State Encoding
Here two parameters are taken into account :
Expected number of bit transitions.
Expected number of transitions of output signals.
Consider the figures shown below which represent functionally identical state machines M1 and M2 with different encodings.
Design trade offs in State Machine Encoding
State encoding affects power dissipation as well as area of the machine.
Problem 1 : It is very difficult to find the encoding technique that minimizes the state-bit transition E[M].
Problem 2 : Logic synthesis system can perform automatic state encoding for area minimization but it may not be desirable for power dissipation because the expected transition is high.
Problem 3 : If states are encoded to minimize power dissipation , the area has to be increased.
One solution to above problems is to use a subset of states that spans high probability edges i.e encode the state incident to high probability edges to reduce E[M].