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one hot ? or two hot state machines - explanation needed

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noldsworth

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one hot ? or two hot

Hello,

I usually do moore state machine at university. However during my internship, people are talking about one-hot and two hot statemachines. I was able to create one-hot statemachines from a template. However I don't understand what does "one-hot" mean. Can anyone shed some light please ?
 

haneet

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Re: one hot ? or two hot

it is a concept where the the transition from present state to next state would happen with a one bit change of the state

ex:

00, 01, 10, and 11 are the states then the state transition shld be
00-->01 ---> 11 ---> 10 or such similar one bit change combination.

Please correct me if i am wrong.

regards,

Haneet
 

RBB

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one hot ? or two hot

Yes. You're wrong. One hot mean only one bit it active at a time, i.e.
state 1 00001
state 2 00010
state 3 00100
state 4 01000
state 5 10000
etc.

One-hot state machines can be more fault tolerant & reduce the amount of next and decode logic. But us8ally they are larger.
 

skyfaye

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Re: one hot ? or two hot

One-hot encoded FSM typically requires more FF but less combinational logic than other types of FSM. In my 10-years of ASIC/FPGA design experience, I find one-hot encoded FSM to be most often used. The main reason is probably because your design can better meet timing due to less combinational logic.

By the way, I think you're confuse with the difference between moore/mealy and one-hot and other type of encoded FSM. Moore/meally is a type of FSM, where as, one-hot is a way to encode the states of a moore/meally FSM. So you can have a moore FSM with one-hot encoding, binary encoding, or other types of state encoding.

- Hung
 

svhb

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Re: one hot ? or two hot

One-hot state machines can be more fault tolerant

Only if you add a check on the number of ones set, I think.
 

vivek_p

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What about the power of one-hot state encoded state macines?
 

k12345k12345

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Onehot simply means that only one bit of the states put together is high - meaning only one state is active.

Only one bit changing is gray code.
 

vivek_p

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Does one hot state encoding reduce power consumption.................How?
 

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