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Schematic Symbols for Integrated Circuits

July 20, 2020The SnapEDA Team

Pin naming, pin setting, and pin arrangement are the 3 most important factors to consider in creating a good symbol for your IC devices, being the primary element in schematic drawings. These factors will help designers create a direct and functional design to produce the desired electrical behavior.

At SnapEDA, after many years of feedback collection and investigation, we developed our own internal standards based on the 3 factors to provide the best symbols PCB designers could use.

PIN NAMING

As they say, always get the name right! 😉

To avoid incorrect pin mapping and unwanted connections, make sure to name your pins correctly based on the datasheet. It is recommended to include the names of the alternate functions per pin. However, if there are too many functions and you prefer a smaller symbol you can just use the main pin name.

PIN SETTING

Know the directions so you won’t get lost! 🤭

Don’t forget to set the electrical type or direction of the pin (I/O, Input, Output, Power, Passive, Power Input, Power Output, Open Collector, Open Emitter, etc). If pins are not defined properly ERC may not work as expected. Some examples are:

  • Power pins like VCC or Ground = Power
  • Reserved pins or shield pins = Passive
  • NC pin = Not Connected
  • P0.0, P0.1, P0.2 = Input/Output or Bidirectional
  • Chip Select pin = Input

In addition, always set the pin functionality which is known as graphic style in KiCad or symbol pin in Altium Designer and it allows you to add the electrical characteristic of a pin (Clock, Inverted Clock, Input Low, Active Low, etc). Please take note it is preferred not to set the functionality for pins with multiple functions (ex: GPIO3/SCLK/INT/DO)

PIN ARRANGEMENT

Organization is key! 🗝️

The pin direction is the first element to be considered when arranging your pins. SnapEDA follows a mix of IEEE-315 and our own internal standards for symbols, based on our internal standard we recommend these positions:

  • Place Input pins at the left
  • Place Output pins at the right
  • Place I/O pins at the middle left (if there are too many I/O pins, place some at the middle right)
  • Control pins can be placed at the upper left
  • VCC or power pins can be placed at the upper right
  • Place GND pins at the lower right

While it is an organized method to arrange the pins based on their directions, it is not the only element to be considered in arranging your pins. It is very important to know the function of the whole device and the function of each pin to have an operative symbol for your schematic diagram. Arrange pins logically based on their functions as well, which can be determined by checking the pin description, the circuit diagram, or the function diagram.

OTHER TIPS

A little extra for you! 💌

  • If your symbol has +100 pins, separate the symbol into multiple sections based on functionality (PartName_Power, PartName_I2C, etc)
  • Do not include NC pins (not connected/no connect pins) in the symbol unless it has an alternate function
  • If exposed pads or thermal pads are present, add an EXP pin
  • If reserved pins are present and can be connected or left floating, add an RSVD pin

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ATMEGA328P-AUR

Create your schematic symbols based on these 3 factors and you’re good to go!

The SnapEDA Team Administrator

Parts as fast as lightning ⚡️The best way to discover and design-in electronic components. www.snapeda.com

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