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Subject: Allegro Electrical Constraint Spreadsheet
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andrewsr
Posts: 13
Online: User is Offline
5/03/2007 4:33 AM  
Does anyone actually use this? I normally just set up line widths, spacing and so on by layer using the "Extended design rules". I was playing with it a couple of times trying to assign diff pairs and it gave me nothing but trouble. It crashed once and when it didn't crash it didn't want to route the pairs as I thought it should have. Maybe I just need to work with it more or take some training.
Just wanted to get others opinions on the subject.
Kalevi2
Moderator
Posts: 69
Online: User is Offline
5/03/2007 4:58 AM  
Andrew:

Constraint driven design is used by most designers. The constraint manager is absolutely essential to getting things right on anything but the simplest PCB. Our layout folks do not like to use the single ended impedance constraints but relative prop delay, diff pair, min/max prop delay, and wiring are used all the time by us. I don't know of any serious PCB Layout service bureau or OEM in-house layout group that does not use constraint driven design and when using allegro, the constraint manager. Cadence offers a 1 day constraint manager course that is really usefull in getting up to speed on the tool.

The normal flow is that the board electrical designer enters as many constraints as he can in during the schematic capture and then he (or she) or the signal integrity engineer enters the rest in constraint manager after schematic is complete and pre-layout simulations and timing analysis have been completed.

Crashing was pretty common on versions of the tool before 15.7. You might want to check that you have the latest ISR installed for your version.
Kai Keskinen
BrianA
Posts: 0
Online: User is Offline
5/03/2007 5:19 AM  
Is the 1 day Constraints course that Cadence offer a Webinar course?

BrianA
Kalevi2
Moderator
Posts: 69
Online: User is Offline
5/03/2007 5:35 AM  
The course I'm referring to is a 1 day instructor led course. Allegro also comes with two CM tutorials, front end and back end.
Kai Keskinen
mcatramb91
Posts: 141
Online: User is Offline
5/03/2007 5:36 AM  
It took some time for us to get use to using Constraint Manager but now we use it all the time. We have Viewdraw on the front end for schematic capture so we have a whole process around adding the net properties on the schematic side and passing it forward to Allegro which has been doing it for a very long time.

We have been slowly shifting the design management activities over the Constraint Manager because it is becoming a pain to manage design rules without it. Of course some things can only be managed in Constraint Manager like Extended nets (XNETS) which allow you to define rules from IC to IC looking thru discrete component.

Mike Catrambone
UTStarcom, Inc.
mcatramb91
Posts: 141
Online: User is Offline
5/03/2007 5:43 AM  
To get an idea how Constraint Manager works you could check out the webinar achieve on cadence.com

http://www.cadence.com/products/si_pk_bd/demos.aspx

They certainly won't replace an actual course but it will at least give you some background information.

Mike Catrambone
UTStarcom, Inc.
andrewsr
Posts: 13
Online: User is Offline
5/03/2007 2:10 PM  
Thanks for all the quick replies.
bforsse
Posts: 1
Online: User is Offline
8/29/2007 5:22 PM  
Are there any PDF user guides for Constraint Manager? Or is there any documentation that explains the difference between the constraint options inside Constraint Manager?

Thanks,
-Brian
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