Why is it that the ERC tool generates warnings for POWER pins that are
connected to SUPPLY pins?
I know I can approve them but I still find it odd since in my opinion
device's POWER pins are precisely intended to be connected to SUPPLY pins
but apparently Eagle has a different opinion in this respect.
Robert
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Robert Blancquaert schrieb:
Why is it that the ERC tool generates warnings for POWER pins that
are connected to SUPPLY pins?
I know I can approve them but I still find it odd since in my
opinion device's POWER pins are precisely intended to be connected to
SUPPLY pins but apparently Eagle has a different opinion in this
respect.
Basically, you're right - but ERC does not complain about this, but
about the different net names.
A supply pin implicitly forces the attached nets name to that of the
symbol (say GND, VCC, +24V etc.). A power pin implicitly connects to a
net that matches its name, so it "wants" to be connected to this
particular net name.
If you connect a power pin with the name VCC to a supply net with the
name +5V (for example), ERC complains about this. This has always been
that way, and is boring from the day when these pin types and ERC were
introduced - particularly when you're mixing different device types
(analog, digital, several voltage rails) in a design.
To be fair, there's no clean and easy way around this, unless EAGLE
would simply ignore the names of power pins - but then, you can as well
declare them as "passive" in the symbol... (That's what I do in symbols
that will be used at very different supply names.)
So at the end, it's fine that you can just "approve" these warnings. 
Tilmann
Robert Blancquaert schrieb:
Why is it that the ERC tool generates warnings for POWER pins that
are connected to SUPPLY pins?
I know I can approve them but I still find it odd since in my
opinion device's POWER pins are precisely intended to be connected to
SUPPLY pins but apparently Eagle has a different opinion in this
respect.
Basically, you're right - but ERC does not complain about this, but
about the different net names.
A supply pin implicitly forces the attached nets name to that of the
symbol (say GND, VCC, +24V etc.). A power pin implicitly connects to a
net that matches its name, so it "wants" to be connected to this
particular net name.
If you connect a power pin with the name VCC to a supply net with the
name +5V (for example), ERC complains about this. This has always been
that way, and is boring from the day when these pin types and ERC were
introduced - particularly when you're mixing different device types
(analog, digital, several voltage rails) in a design.
To be fair, there's no clean and easy way around this, unless EAGLE
would simply ignore the names of power pins - but then, you can as well
declare them as "passive" in the symbol... (That's what I do in symbols
that will be used at very different supply names.)
So at the end, it's fine that you can just "approve" these warnings.
Tilmann
