[PCB_FORUM] Re: Schematic drafting practices

I guess I'll have to defend the honor of at least SOME of us engineers...

Those of us who grew up actually DRAWING schematics (with pencil and paper, not 
a mouse!) learned about signal flow and organization, especially in a day when 
a schematic had more than one or two ICs on it.  (Think 74-series MSI TTL and 
the early PAL/GAL programmable logic devices.)

(Ok, disclaimer here:  I finished my BSEE in 1974 and MSEE in 1978, so yes, I 
started out with paper and pencil for schematics and tape on mylar for layouts. 
 Call me a dinosaur...guilty as charged, Your Honor.)

Your best bet is probably a DIY approach.  Show them some well-organized 
schematics with proper left-to-right signal flow and most engineers are logical 
enough to pick it up fairly quickly.

Others are untrainable...I'll admit that...

We have started several times to define schematic-drawing conventions but it 
seems that about the time we get a decent draft, the technology changes enough 
that it messes up our strategy.  (That includes simple but critical things like 
signal naming conventions, which have been changed several times on us as we 
moved from Cadentix to Valid to Cadence to Orcad plus all of the various EPLD 
software we've used over the years.)

Your best bet is to get them to think of a hierarchical organization of their 
designs and grouping functionally-related components together.  Then start off 
with the simple stuff...inputs on the left, outputs on the right.  Some things 
(like good visual layout) are tough to teach...either they understand 
intuitively or they don't and it'll never sink in.  The other stumbling block 
is an unwillingness to add just ONE MORE PAGE to the schematic so you can 
un-crowd the pages and make them all more readable.  (Or, you can take that to 
the opposite extreme like the IBM System/7 schematics that I had to work on in 
grad school.  One register or one small block of logic per page with umpteen 
inputs and outputs to several other pages.  Those were HORRIBLE and they came 
from Big Blue!)

...should be an interesting discussion...

/s/jar (Alan Ritter, alan.ritter@xxxxxxxxxx)
        http://www.mtritter.org




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