[PCB_FORUM] Re: Metric to English - English to Metric

 
The question remains:
 

WHY switch back and forth?

 
If the board is started in one unit, you are making it harder on yourself
and others switching back and forth, even with NO round off errors.  The
grids are different, the trace widths are different (unless you LIKE typing
two decimal places all the time).  It is senseless to be switching it
around, unless it is just to make extra work for yourself or your
international partner.  Why not just KEEP IT SIMPLE (K.I.S.S.) :)
 
-- 
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272         Fax: 503-627-5587 <http://www.tektronix.com/> 
http://www.tektronix.com     <http://www.pcb-designer.com/>
http://www.pcb-designer.com

It's my opinion, not Tektronix' 

-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Patrick Jabbaz
Sent: Wednesday, August 24, 2005 14:58
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric



Here is the trick to make it work, In Allegro,

You can switch units from metric to mils, and vise versa without errors, if
you have the following setup:

User Units mils use 2 decimal places 

User Units  millimeter  use 4 decimal places

Using this process, allows you to switch back and forth without any round
off errors.

Patrick Jabbaz

Sr. PCB Design Eng.

Xilinx

2100 Logic Drive

San Jose, Ca 95124

Direct: 408-879-4709

M: 408-621-6533

email: patrick.jabbaz@xxxxxxxxxx

 


  _____  


From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
Sent: Wednesday, August 24, 2005 2:26 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric

 

Hi Richard,

 

Perhaps more than a decade ago, the CPU and code speed may have been an
issue.  But, in the realm we are talking about (a printed circuit board and
the range of numbers and precision necessary) IMO and IME the compiler
imposes no significant restrictions, nor does the "math processor" in the
CPU.  Again, it is simply a matter of knowing where the decimal point is.

 

In Allegro, you don't convert because the tool can not handle it.  In a tool
that can adequately handle it, this is not an issue.

 

Regards,

 

Austin 

 

 -----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of richard moffat
Sent: Wednesday, August 24, 2005 5:15 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric

Cadence is probably making a compromise for speed.  The way that other tools
may allow a seemless interchange is to have a greater length of significant
numbers in the internal database, especially converting metric->imperial.

 

The programmers are restricted to that they are given:  The C compiler, and
the maths processor on the CPU.

 

In short:  don't convert!


>>> austin@xxxxxxxxxxxx 25/08/2005 9:08:15 a.m. >>>

Hi,

> Conversely, 1/10 (0.1) cannot be exactly represented in base 2...

I design ASICs, and I have done a LOT of arithmetic functions in ASICs, and
use decimal points all the time.  All hardware arithmetic functions are done
in base 2.  It's simply a matter of knowing where the decimal point is and
using enough digits.  Yet, it goes on to explain the solution (as I said,
knowing where the decimal point is)...so I fail to see the *real* problem.

As was pointed out, PADS has no problem switching back and forth between the
two unit systems, so I simply don't believe Allegro can't do it as well.  It
seems like this may be a self imposed restriction:

> The real issue is that some numbers can't be represented exactly in the
> standard floating point representation.

Why do they have to use "standard" floating point representation anyway?
Sounds like someone programmed themselves into a corner, and instead fixing
it, they are trying to come up with explanations...instead of solutions.
Sigh.  To me, this is a huge weakness of Allegro.

Regards,

Austin

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