When drawing a circuit in a schematic editor, most of the time people are going to have to draw their own custom symbols, for example ICs.

What is the standard practice for the way in which pins are laid out on a custom symbol?

  1. Is it better to order the pins around the block as they appear physically on the part....(I find this helps with pin identification when debugging hardware)Symbol example 1

or 2. Is it better to assume a non-chronological order so as to minimise cross overs of wires...(I find this helps improve readability)Example of Symbol 2.

Summary: Which of those two methods (or another i'm unaware of) considered standard practice?

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    \$\begingroup\$ Somtimes it's useful to draw a block of the innards or overlay an image, for example this, to pick the most hated part. Spending more time on the symbol usually pays off in readability. \$\endgroup\$ – Spehro Pefhany Jan 17 '18 at 17:52
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    \$\begingroup\$ I generally like grouping by function, closer to your second diagram. However I do find merits in the schematic diagram following the package, especially when choosing pins so that I don't choose two pins on opposite sides of the package when I could select one closer (for example when routing serial lines). \$\endgroup\$ – Ron Beyer Jan 17 '18 at 19:39
  • \$\begingroup\$ @SpehroPefhany where would you draw the line for such an overlay, presumably for a uProcessor you wouldnt do this? \$\endgroup\$ – Pop24 Jan 18 '18 at 8:57
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    \$\begingroup\$ The general flow of schematic is from left to right and top to bottom. For the second type, keep to inputs on left, outputs on right, vcc on top and gnd on bottom. This might be helpful electronics.stackexchange.com/questions/28251/… \$\endgroup\$ – Hemal Chevli Jan 18 '18 at 11:49

You draw symbol the way your circuit is best readable and understandable. Techniques used are:

  • grouping pins into busses;
  • having space between pins groups per their purpose, usage or their connect destination;
  • making comprehensive labels on the pins and on the devices.

From my experience reading circuits drawn using packages is a nightmare. Packages belong to board layout, not to schematic diagrams.

You may also find drawing circuit diagrams using packages inconvenient. There's always a choice for new device: make quick shortcut and reuse existing package as symbol, or draw own symbol, which takes time and real knowledge of device operation and pin purpose. I used to take time and draw new comprehensive symbol, and split large devices into logical blocks (symbols) for readability.

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    \$\begingroup\$ The point about getting to know the component when making the symbol is more important than it might seem \$\endgroup\$ – MrGerber Jan 17 '18 at 17:35

Both methods are used, therefore both are "standard".

Which one you should use is a matter of opinion, and a decision about which one better conveys the necessary information to the person reading the schematic.

For the person trying to understand the logical operation of the circuit, grouping the pins by function is usually better.

For the person using the schematic to figure out where to probe the circuit when debugging it, arranging the pins by their physical location is usually better.

As the guy drawing the schematic, you simply can't please everybody.


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