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

Hi Kanak,
Someone made an interesting suggestion yesterday. When you must switch
back and forth, set the accuracy in millimeters to 4 decimal places, and
the mils to 2 decimal places. Apparently this removes the rounding
errors. I haven't tried it my self, but it's worth a try if you need to
use this approach.
Andrew

        -----Original Message-----
        From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Kanakaraj
        Sent: Wednesday, August 24, 2005 9:11 PM
        To: icu-pcb-forum@xxxxxxxxxxxxx
        Subject: [PCB_FORUM] Re: Metric to English - English to Metric
        
        
        Hi,
         
        In my project, the customer has given the mechanical dimensions
of the connectors and mouting holes in mm. ( with three digit accuracy
like 21.213 mm). I place the connector with milimeter as measurement
unit and switch back to mils for routing.
         
        When we are doing the dimensioning, we again switch back to
milimeter, then we encounter errors upto two decimal points. ( the
connector fixed at 21.213mm is showing as 21.192 mm.. for an example).
         
        have any one encountered issues like this? how can this be
fixed.
         
        Regards
        ~Kanak
         

                ----- Original Message ----- 
                From: george.h.patrick@xxxxxxxxxxxxxx 
                To: icu-pcb-forum@xxxxxxxxxxxxx 
                Sent: Thursday, August 25, 2005 3:39 AM
                Subject: [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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