FSM Encoding algorithm

[yaser123]

fsm encoding algorithm

hi all
what's difference b/w One-Hot Encoded Finite state machin and Binary-Encded FSM?and why does former is suitable for FPGA and later for CPLD desogn?
tnx ahead

 

[eda_wiz]

fsm one hot

onehot encoding: The number of FFs used is the same as number of states in the FSM. say a 31 state fsm will be having 31 flops after synthesis.

only one flop will be active ("hot") in a state.

Adv. Low power(since only one toggle when state changes), simple decoding logic.

Binary encoding will take n flops for 2^n states.
so 31 state FSM will take 5 flops.
Disadv. decoding logic is complex.

popular method is onehot.
FPGA has lot of registers compared to CPLD. so onehot is more suitable for FPGA

Hope it helps

 

[semiconductorman]

one hot fsm

One Hot is also a bit faster than binary if the number of fsm stages are big . Can be explained by the point that whizkid has put . Decoding is simple , suppose there is a fsm with 31 stages then for binary encoding a lot of levels of decode logic is present but for one hot encoding decode logic is very less .
On Area One Hot takes a bit of a more area since flipflops generally have more area consumption than combination logic .This can't be generallised and denpends on the number of transisitons in your statemachine , but usally this is the case

 

[yaser123]

fsm encoding

tnx friends
but how a bout other algorithm like compact , johnson...?
tnx again

 

[ikru26]

two hot encoding

check this attacehd powerpoint slide....

 

[Ace-X]

two-hot encoding

I would suggest to check manual for any synthesizer. For example, you can get Leonardo Spectrum guide here: **broken link removed**

It has very clear and comprehensive description of different FSM encoding styles, including One Hot, Two Hot, Gray, Binary etc.

Check section "Enumerated Types" for details.