Connect all VCCs and GNDs?

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I am laying out my first PCB with a ATmega16 in a TQFP package. I want to know if it is necessary to connect all of the VCCs to 5V and all of the GND to ground? Or are the connected internally and connection of only one set is necessary? Thanks.

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You should make all the connections to produce the most stable / reliable behaviour of the AVR with the least EMR etc etc.

In practice it will work ok without.

A bit like comparing a breadboard ratsnest to a perfectly designed pcb. Both probably work. If the breadboard gives a problem, you know why.

David.

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Even if it would work without connecting all the supply pins, it will limit maximum current you can feed to AVR so you have less current available on IO pins.

So in practise, do what the datasheet says. Datasheet may look big and scary, but in the end, it is just a guide that says "if you do things like this we guarantee it works. if you don't do things like this, nobody knows how it will behave".

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Alright thanks for the help. I'll connect them up and send out the board.

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You probably also want to read AVR040 and AVR042 (I think those are the numbers!)

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Isn't one of the ports supplied by a separate VCC? VCCA or so?

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On most AVRs (apart from mega8) with ADC pins it's the port with the ADC that needs AVcc to be connected so it's powered. (on smaller devices, like mega16, this is often PORTA)

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fiebigc wrote:
I am laying out my first PCB with a ATmega16 in a TQFP package. I want to know if it is necessary to connect all of the VCCs to 5V and all of the GND to ground? Or are the connected internally and connection of only one set is necessary? Thanks.

remember to put a 100nF cap , on each power/gnd pair

/Bingo