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The Designer's Guide Community Forum › Simulators › AMS Simulators › How to force an unknown state to 0V or 1.8V?
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How to force an unknown state to 0V or 1.8V? (Read 2262 times)
Kamal
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How to force an unknown state to 0V or 1.8V?
Sep 23rd, 2011, 1:37am  
Hi all,

I am running mixed simulations with AMS-ADE and I have an unknown state on one output of a digital block (output of a flip-flop before the reset).

How to force this unknown state to 0V or 1.8V?

During the simulation I use the "ConnRules_18V_full_fast".
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boe
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Re: How to force an unknown state to 0V or 1.8V?
Reply #1 - Sep 23rd, 2011, 1:57am  
Kamal,
There are several options, you could e.g. change your connect module or use the force/release commands to override the signals at the beginning.

B O E
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Kamal
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Re: How to force an unknown state to 0V or 1.8V?
Reply #2 - Sep 23rd, 2011, 3:00am  

Thanks for your answer BOE, however could you be more explicit.
In fact, I am a beginner with mixed-simulations & AMS.

In the "Cadence AMS Simulator User Guide" there are force Command Examples but I do not understand how to use those commands in ADE.
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boe
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Re: How to force an unknown state to 0V or 1.8V?
Reply #3 - Sep 23rd, 2011, 4:33am  
Kamal,
If you use interactive simulation mode (Netlister & Run Options) the simulator starts with GUI, so you can enter commands in the console.

B O E
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Kamal
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Re: How to force an unknown state to 0V or 1.8V?
Reply #4 - Oct 6th, 2011, 7:20am  
Hi Boe,

I have following message when I try to use "force" command:

ncsim> force {test_Pll.I0.I0.I2.I31.vcofc_out} 4'b1010
ncsim: *E,SETAIA: Analog engine is active. Cannot force digital object: test_Pll.I0.I0.I2.I31.vcofc_out.

Any idea of the meaning of this message?

K.
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boe
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Re: How to force an unknown state to 0V or 1.8V?
Reply #5 - Oct 6th, 2011, 7:37am  
Hi Kamal,
try Code:
run -sync
before the force command. This should advance to the next time point where digital commands are permitted.
B O E
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Kamal
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Re: How to force an unknown state to 0V or 1.8V?
Reply #6 - Oct 6th, 2011, 8:32am  
Thanks Boe for your help, you command "run -sync" works.
I have a last question, do you know how to release the digital outputs after few nano seconds (10ns)?

K.
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boe
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Re: How to force an unknown state to 0V or 1.8V?
Reply #7 - Oct 6th, 2011, 8:39am  
Hi Kamal,
Code:
run 10ns
run -sync
release ...
B O E
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Kamal
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Re: How to force an unknown state to 0V or 1.8V?
Reply #8 - Oct 7th, 2011, 6:00am  
Thanks BOE.
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loose-electron
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Re: How to force an unknown state to 0V or 1.8V?
Reply #9 - Oct 29th, 2011, 6:06pm  
why not use an initial conditions definition?

undefined state is not always a bad thing, your test routine probably hits the "reset" early in the test bench anyhow.
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boe
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Re: How to force an unknown state to 0V or 1.8V?
Reply #10 - Nov 1st, 2011, 4:22am  
Jerry,loose-electron wrote on Oct 29th, 2011, 6:06pm:
why not use an initial conditions definition?
Because the standard CMs are essentially a voltage source converting 'X' to VDD/2. This can be awkward even if it does not need to be "a bad thing", as you correctly pointed out.
- B O E
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