EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Thewafflication on May 16, 2018, 01:19:00 am
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(I think I am in the right place...)
I am creating a schematic for a one project that I am working on, but one component is not available in the KiCAD library. I am attempting to create my own, but would like some guidelines for style.
The chip is a 100 pin LQFP uController. (MSP432P401RIPZ)
I am considering a couple different possibilities:
1. Split the uC into multiple parts.
2. Put the pins into two rows.
3. Arrange the pins, in a square, like the the package.
I just want to ensure my schematic is easy to follow.
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My personal preference is two vertical rows. Parts up to 144 pins looks fine when done like this. I don't like huge empty squares, since they take up a lot of space.
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I tend to agree with Ataradov. The slim symbol with two columns of pins (and maybe a few out each the top and bottom) wastes the least space. I definitely don't like splitting the chip up to several "gates" or symbols so that they can be used on several pages. Some people do. I used to work for a company that did this and had to employ a person dedicated to the job of creating a different set of symbols of the same chip for each and every project the chip was used on. It slowed schematic creation by the designer as well. :rant: And if the designer decided to move a function from one symbol to another then the whole point of the exercise was lost.
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Split it into multiple parts and make separate schematics for power, I/O, USB, etc.
I like using https://github.com/xesscorp/KiPart (https://github.com/xesscorp/KiPart) which allows entering pins (SCK, VCC, P2.0, etc), units (A, B, C...), edge (up, left, etc) and pin functions (input, passive, power, etc) in a spreadsheet, export it as a csv, and convert that to a KiCAD component using that little tool. Then edit the component to clean it a bit if desired. It's very quick and easy, but takes a bit of practice. Excellent for splitting complex parts like this based on function and arranging pins for schematic fit.
The original 144 pin component in the datasheet is convenient for planning pin functions and PCB layout. Sometimes there isn't one in the datasheet (IMO a major documentation deficiency); in that case I simply create one using a spreadsheet and KiPart and print it. Usually there is at least a pin table; that can reasonable easily be copy-and-pasted and converted to a csv file then imported into a spreadsheet for editing.
Once I have a pin plan I copy and edit the single-unit monolithic component and make it a multi-unit component (which is really just changing values in the spreadsheet), generate the component using KiPart, create hierarchical schematics, and place the parts.
Hopefully at some point they'll add direct editing of a component pin table, including moving pins between units.
Here's an example with an LPC4078. As you can see the pin functions are pruned to those relevant. The ones on the main I/O header have kept most functions since this is a prototype board.
(http://www.rockgarden.net/download/eevblog/sky_blue_io.png)