Re: gEDA-user: Method to create symbol for enhanced ICs with many pins

[Kevin Vermeer <reemrevnivek@xxxxxxxxx>]

> Tamas Szabo <sza2king@xxxxxxxxxxx> writes:
> I would create a schematic symbol for AT91SAM7 device: 64 pins, lots
> of them with multiplexed functions.
> 1. I can number pins round, 1 to 64 sequentially:
> [snip]
> 2. I can separate pins by functions, without keeping the pins' order:
> [snip]
> Furthermore, since the above mentioned device has at least 3 function
> for 32 pins, it is more difficult to setup a suitable pin placement
> applying the second option.

It is only really difficult if you're working on a breakout board or
other generalized schematic, and have to try to make all possible
configurations look good.  A normal project will have these
peripherals hardwired to a peripheral using only 1 of their functions,
so it's a very easy task to organize the pins logically.

> By the way, I saw the first option in many places (for example my company
> also provide schematic this way).

In my estimation, the reasoning behind this practice is not because
it's the most logical, but because it's the easiest to execute and to
coordinate.  The draftsman doesn't have to make any decisions and
different symbols from the same company by different draftsmen will
all look the same.

> However, since in my opinion schematic is a logical thing, I prefer the
> second option.
> Which is the better solution?

I agree that the schematic is a logical thing, and prefer the second
option, but in the end it's a matter of personal preference.

I'd suggest grouping the pins by one of two functions: PIO/Peripheral
vs. chip management.  Some, like JTAG and USB (if you have that) could
go on either side.  The power side will largely stay the same between
projects.  On the other side, you can either order the pins by their
GPIO number, or group them by peripherals.  See an example of the
former by Bob Starr for the Eagle library here:
http://imgur.com/D96os.png - as you said, it will be hard to do the
second in a general manner.  If you want to try, I'd suggest using the
chip block diagram on page 5 of the datasheet as a starting point.

My preferred method, Option 4, would be to make one symbol like the
linked image, and then shuffle the pins around for your project.
Then, when you have a different project with different peripheral use
patterns, it's easy to copy the symbol and move the pins around into
the grouping that fits your project. Save the master symbol in your
global symbol folder, and the customized symbols in each project
folder.  This does make comparing schematics between projects more
difficult, but it's likely that the peripheral you're investigating in
this case will be grouped in both schematics.
--
Kevin Vermeer


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