[PCB_FORUM] Re: Propagation Rules driven from Schematic to Allegro

Hey Dale,

 

Here's how I do it:

 

1)      All net names for diff pairs should have a standard naming
convention. We use a suffix of "_P" and "_N" (i.e. "USB1_P" & "USB1_N").

 

2)     Set up the diff pairs in Allegro using Logic -> Assign
Differential Pair, Auto Generate. With Auto Generate, you enter your
common suffix for + and -.

 

3)     Now in Constraint Manager, they will show up under Differential
Pair (tab at bottom)

 

4)     The Phase Tolerance/Tolerance column is where you enter the
tolerance for the length of the P to N within each diff pair (25 mils in
your case).

 

 

Now the second part, having the 20 pairs in a group; are you saying that
you want these 20 pairs to be 1000 to 2000 mils in length?

 

If so, you could use the Total Etch Length tab, use Create -> Bus to
group all of the N and P nets for the 20 pairs and then enter 1000 for
Total Etch Length/Min, and 2000 for Total Etch Length/Max.

 

I have not had to match a bunch of diff pairs to a min and max length
yet, but it sounds like it should work.

 

Good luck!

 

Gary

 

  

Gary E. MacIndoe
PCB Design Engineer
Fort Collins, Colorado

amd.com

gary.macindoe@xxxxxxx

________________________________

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Dale Rasmusen
Sent: Friday, April 25, 2008 12:55 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Propagation Rules driven from Schematic to Allegro

 

Hi all, I was wondering how to do the following...  

 

I have diff pairs that need to have REL_PROP_DELAY GRP:G:L:S::25
properties between P and N signals.. but I also want to place 20 of
these pairs in a group that must adhere to a PROP_DELAY of
L:S:1000:2000.

 

Thus I have P and N constraints as well as a group prop delay
constraint.

 

I'm not sure how to structure these rules for Allegro.  Your help is
appreciated.

 

Thanks,

 

 

Dale Rasmusen

CAD Manager

TEKNOVUS

(707) 665-0400 ext 133

(707) 665-0491 fax

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