Algebraic loop on not-1098 detected.

Altair Forum User

 

Submitted by Joe on Fri, 09/30/2011 - 02:52 

 

I think VisSim doesn’t like the fact that the speed variable, which is downstream from the NOT block, is wrapped around to be one of the inputs before the NOT block. In a strictly digital simulation, this could cause a problem, but even then, you could have examples where outputs are wrapped around to eventually be inputs to a given logic block (e.g., a SR latch).

At any rate, if I ignore the warning message, the simulation works just fine. My question is, is there any way to tell VisSim not to display this warning message?

Altair Forum User

Submitted by Anders89 on Fri, 09/30/2011 - 02:57.

 

 

Joe, this is a common problem with VisSim beginners. The issue is that you have no delay block (1/s, 1/z, transferfunction, timeDelay) to break the loop. Without any delay, there is no specified place to start calculating the loop. VisSim is left to it's own devices to pick a starting point and it may give results you expect, but it may not, depending on it's choice of execution order. We have a very good whitepaper on algebraic loops here.