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Simulators >> AMS Simulators >> How to force an unknown state to 0V or 1.8V?
https://designers-guide.org/forum/YaBB.pl?num=1316767053

Message started by Kamal on Sep 23^rd, 2011, 1:37am

Title: How to force an unknown state to 0V or 1.8V?
Post by Kamal on Sep 23^rd, 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".

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by boe on Sep 23^rd, 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

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by Kamal on Sep 23^rd, 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.

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by boe on Sep 23^rd, 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

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by Kamal on Oct 6^th, 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.

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by boe on Oct 6^th, 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

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by Kamal on Oct 6^th, 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.

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by boe on Oct 6^th, 2011, 8:39am

Hi Kamal,

Code:

run 10ns
run -sync
release ...

B O E

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by Kamal on Oct 7^th, 2011, 6:00am

Thanks BOE.

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by loose-electron on Oct 29^th, 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.

Title: Re: How to force an unknown state to 0V or 1.8V?
Post by boe on Nov 1^st, 2011, 4:22am

Jerry,
loose-electron wrote on Oct 29^th, 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