[PCB_FORUM] Re: Metric to English - English to Metric
- From: "Patrick Jabbaz" <patrick.jabbaz@xxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Wed, 24 Aug 2005 15:14:26 -0700
George,
I partially agree with you, most of the time there is no need to switch,
however, there are times that you need to load a mechanical DXF that was
design in metric, or to double check some dimensions, and it is nice to
switch for the special occasions.
-Patrick
________________________________
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of
george.h.patrick@xxxxxxxxxxxxxx
Sent: Wednesday, August 24, 2005 3:09 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
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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