[PCB_FORUM] Re: Constraint Manager - difference between "
- From: "Leonard E Toohey (ltoohey)" <ltoohey@xxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Mon, 7 Mar 2005 09:26:35 -0600
total etch length does not consider the package or pin delays
prop delay does consider the package or pin delay.....
_____
From: Andy_Kulik@xxxxxxx [mailto:Andy_Kulik@xxxxxxx]
Sent: Monday, March 07, 2005 7:54 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Constraint Manager - difference between "
Austin,
For all 2pin nets/xnets use Total_Etch_Length (TEL). The router just loves
it. All net/xnets above 2 pins use min/max propdelay rules. Think pinpairs
or drivers/receivers for these types of nets. Picture a xnet with one driver
and 3 receivers. The length from the driver to each receivers needs to be
the same.
TEL doesn't get you anywhere here. You need to implement constraints based
on the pin pairs of the net....
I wrote a tutorial which was handed out to attendees at the local Cadence
users meeting in February in Massachusetts. Contact me directly and I will
forward it to you and others who are interested. It covers the basics and
explains what to do and what not to do in order to master CM and SigXp and
is based on SPB15.2
Best Regards
Andy
andy_kulik@xxxxxxx
andreas_kulik@xxxxxxxxxxx
Austin Franklin
Sent by:
03/06/2005 11:42 PM
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[PCB_FORUM] Re: Constraint Manager - difference between "
Hi Michael,
> Propagation Delay is mainly used to verify the length or time between
> Pin Pairs on a net where as Total Etch Length is used to control the
> length of the entire net by adding up all the segments.
Thanks, I think I understand what you are saying the difference is. "Total
Etch Length" add up ALL the tracks, including branches. For a two pin net,
essentially the two would be the same, but with three or more pins on the
same net, then they are different.
If my understanding is correct, I'm not sure what design wise (not
physically on the PCB, that I believe I understand if what I wrote above is
correct, but electrically) a constraint like this would be used for. How do
you come up with the value for that rule?
Regards,
Austin
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