Eeschema - Are all power ports connected together?


#1

Hi there,

I am new to KiCad. I have made a schematic that uses local labels.

Several areas need to be connected to +9V and GND. I have placed power ports at those places. Are all +9V power ports connected together? Are all GND power ports connected together? Do I need to place PWR Flags on every GND power port and every +9V power port, or do I just need 2?

Also I am using the ATmega328 chip. It has 2 GND and 2 VCC pins. Do I need to connect GND and +9V power ports to all 4 of these pins or just 2?

Thanks in advance.


#2

Yes as long as the lables have the same text then they will be on the same net, same goes for all the all of the power and ground symbols.

I place PWR flags on all seperate power nets in the schematic like this off in the corner some place.

If your using a library part that some one else made then likely the pins have the Electrical Type set . The Electrical Rules Check will look to see what net connected to the component what the chip expects to see. If you connect a digital output from one chip to the digital input of the next then most of that work is already done for you, however the ERC does not know if net is power unless you drop the PWR flag on it.

If you edit the power and ground pins on your parts in the Library Editor you can set them yourself

Regarding the power and ground pins on the ATMega328 you really need to read the datasheet to be sure.
http://www.atmel.com/Images/Atmel-42735-8-bit-AVR-Microcontroller-ATmega328-328P_Datasheet.pdf

A quick look shows two GND’s that should be connected together, a VCC for digital logic and an AVCC analog supply for ADC. AVcc is rated the same (±0.3 V) as Vcc so just connect them both.


#3

Yes, always connect all gnd/power pins. On mega you MUST also connect AVCC to something, VCC if you don’t have a filtered VCC.

BUT! Does Atmega328 run at 9V? Pretty sure it is max 6V…


#4

Power symbols are a special hack.
They use hidden power input pins. Hidden power input pins are global labels.

Your atmega symbol hopefully does not have it’s power input pins hidden. In this case you need to connect them with the power symbols.

ERC will likely complain that your power inputs are not connected to some power output pin. (Something like no pin to drive pin.)
This is because a power input pin needs to be connected to a power source (power output pin).
In most cases a pcb is supplied via a connector. Place a power flag at the connector or if you have any passive component in series, after this component.


#6

Thank you very much

for your reply. Is the power and ground labelling correct? (attached image)


#7

Thank you, my mistake. Yes it is 1.8 - 5.5.


#8

Sorry to revive an old topic, but I was having the same problem and this really helped.

As an aside, where are these symbols for V+ and PWR_FLAG?


#10

In Dec 17 I posted:
The symbols discussed are in the “power” library, and note that you place them using the “Place power port” tool. Also note that the PWR_FLAG component doesn’t look like the PWR bar symbol shown here, not sure that that is. And further, the whole hidden power pins functionality is a kludge that’s obtuse to the extent of obscuring the simple task of connecting power pins to a global net that happens to be for power.

2018-10-31 I add:

Readers of this thread might also like this other thread: “Understanding power port components”

… and it does get to the heart of the matter!

[Note 2018-10-31: I deleted the original post from Dec 2017, in which I inadvertantly posted an incorrect link to an unrelated topic.]