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What does it mean to kicad that a pin is driven?

I have a 12V rail connected to a battery positive terminal in kicad. Kicad says the 12V rail is not driven. Why does it say that? In fact, it tends to shift around depending on whenever I redraw the wire and run a design rules check on it. I'm trying to make sure the board has a battery input, when it is drawn up on PCBnew.

DesignRulesFail

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2 Answers 2

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The Electrical Rules Check tries to ensure that everything that is connected to a single net fits together. The quick summary is that a valid net has

  • either power (power_in, power_out) or data (input, bidi, output) pins, not a mixture of them
  • at least one pin that can drive the net (power_out for power nets, bidi or output for data nets)
  • at most one pin that unconditionally drives the net (power_out or output)

So a power network needs exactly one power_out connected to it.

A known limitation is that connectors' pins are defined as passive, because that doesn't immediately lead to a conflict with anything else connected to the same net, so the connector that the power supply is connected to cannot be marked as having a power_out pin to placate the ERC.

The PWR_FLAG pseudo-component provides a single power_out pin, so you can avoid the warning here. The ERC will complain if the same net has two PWR_FLAGs, or a PWR_FLAG and some other component with a power_out pin (such as a linear regulator).

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In KiCad the power nets (grounds and sources) should be marked with special symbol "PWR_FLAG" which is located under "power ports" category.

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  • \$\begingroup\$ Does that need to be applied to every net that has a power port on it? \$\endgroup\$
    – HSchmale
    Commented Jun 4, 2015 at 20:17
  • \$\begingroup\$ Yes, unless it's the same net, of course. \$\endgroup\$
    – Eugene Sh.
    Commented Jun 4, 2015 at 20:19
  • \$\begingroup\$ I add power flags but the problem jumps around to other pins. I cant seem to find a way to fix this. \$\endgroup\$ Commented Jun 5, 2023 at 21:40
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    \$\begingroup\$ @user1584421 I don not know how much have changed since 2015 when this answer was written :) But the power flag applies to nets, not pins. If all the pins are connected to the same power net I would be surprised that different pins connected to it will behave differently. \$\endgroup\$
    – Eugene Sh.
    Commented Jun 6, 2023 at 13:33

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