- 1st August 2007, 15:21 #1

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## What does it mean that FSM state register is one-hot?

What does it mean for the statement below:

"FSM state register should always be one-hot"

Thanks in advance for your help

- 1st August 2007, 15:21

- 1st August 2007, 16:43 #2
## FSM state register?

One hot state machines have only a one signal in the state register is a '1'.

For example

State A: 0001

State B: 0010

State C: 0100

State D: 1000

One-hot state machines can be bigger than normal binary encoded state machines, but the next state decode is usually smaller in a one-hot state machine.

Also notice a one-hot state machine is hamming encoded, so that two bits must change for a valid state transition

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- 2nd August 2007, 03:58 #3

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## Re: FSM state register?

Thanks for your reply RBB.

Let say i have state machine below

State A ( 0 ) : 0000

State B ( 5 ) : 0101

State C ( 10 ) : 1010

Above is my FSM. But i have more than 1 signal have logic 1.

So how can the FSM state register should always be one-hot?

- 2nd August 2007, 03:58

- 2nd August 2007, 04:36 #4

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## Re: FSM state register?

One-hot encoding sets one bit in the state register for each state. For ex, FSM with 16 states required 16 FF`s for one hot encoding.

Each node of the state diagram in one-hot encoding is implemented with one FF. There are lot of unused states in the One-hot encoding. If you use N FF , there will be 2used states , 2**power N**- N states are unused states.**power**N

In your example, to represent 5 , you need to specify 10000 not 0101...and etc..

There are diffrent FSM encoding style including One-hot, are Adjucent encoding, Random encoding, User-Specific encoding, Moore encoding, Binary encoding and etc..

Regards,

Sam

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- 2nd August 2007, 04:36

- 2nd August 2007, 08:37 #5

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## Re: FSM state register?

cool sam

your reply is really helpful.

- 2nd August 2007, 10:17 #6

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## FSM state register?

hi

FSM is the finite state machine is used for control logics.

one hot machine is each state taken one FF ex:-0001

it is reduecd glitch

binary state machine is the taken FF s depend on the state 2N= state ,N is the no .of FF

it is used for reduecd area.

vamsi

Added after 35 seconds:

hi

FSM is the finite state machine is used for control logics.

one hot machine is each state taken one FF ex:-0001

it is reduecd glitch

binary state machine is the taken FF s depend on the state 2N= state ,N is the no .of FF

it is used for reduecd area.

vamsi

- 23rd August 2007, 18:49 #7

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## Re: FSM state register?

The only advantage of using one-hot Fsm is the elimination of decoder...

- 24th August 2007, 10:08 #8

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## FSM state register?

fsm state coding depends on your choice, one-hot use more register but give u high speed.

- 13th January 2008, 04:15 #9

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## Re: FSM state register?

Can One - Hot encoding makes data path short.

If yes how?

- 13th January 2008, 06:07 #10

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## FSM state register?

it relies on how many state your FSM has

when the state number is big and require high speed

then one-hot is a best choice