[PCB_FORUM] Re: Schematic drafting practices

I recall Lockheed Martin (previously Unisys Defense Systems / Minneapolis) 
having a fantastic schematic standard. We did not accept or release a schematic 
which did not meet the requirements ... I believe the standard was developed to 
satisfy Military documentation requirements.

Is there anyone on the list from Lockheed who would have access to that 
standard who might be willing to share some of it's content?

> 
> From: "Ritter, Alan" <Alan.Ritter@xxxxxxxxxx>
> Date: 2009/03/27 Fri AM 09:06:54 CDT
> To: "icu-pcb-forum@xxxxxxxxxxxxx" <icu-pcb-forum@xxxxxxxxxxxxx>
> Subject: [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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