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8bit Limit on Enumerated Type?

 
 
GuruSY GuruSY is offline
Junior Member
Join Date: Sep 2008
Posts: 2
 
      09-23-2008
Hello,

I am designing a logically simple interface to a chip, which requires around 300 states. It could require less but I find copy-and-paste

easier than making counters.

Anyway, I always assign my states using the standard enumerated type declaration and let the synthesizer detect my state machine and encode it,

like so:

PHP Code:
type states is (state0state1, ...... etc.

signal presentstate states;
signal nextstate states

I did a behavioral simulation in Modelsim Version 6.0D, and for some reason this happens:

PHP Code:
time t=i:
presentstate state256
nextstate 
state257

time t
=i+1:
presentstate state0
nextstate 
state1 

As a test I changed my code to go from state0 to state257, and the state machine stays in state0 the entire time. Obviously Modelsim is

limiting the size of my enumerated type to 256. Is their a way to force the use of a larger vector? Or am I stuck doing the state encoding by

hand? I think that I could just ignore Modelsim and let the synthesizer do this, but I am a firm believer in clean behavioral simulations

before I move on.
 
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GuruSY GuruSY is offline
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Join Date: Sep 2008
Posts: 2
 
      09-24-2008
Well I ran the code through a newer version of Modelsim: XE III Starter 6.3c and it worked fine. So I assume that this was a bug in Modelsim SE 6.0D that I was using.
 
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