Building my own board which uses an atmega328p AVR. Whole circuit will be powered with 3.3volts. I am wondering what the TX and PWM pin voltages would be in such case. Would I get 3.3volts from both TX pin and PWM pins or is there an internal regulator which provides 5Volts from those pins?
3.3v.
The chip does not contain a voltage booster. That would be a headline feature if it did (like the ATtiny43, which has a switched cap voltage booster to run off very low voltages), and would make the chip significantly more expensive (note how the '43 is so bloody expensive).
If you need 5v output, somewhere you need 5v on the board (from a 5v supply or a boost converter - these can be had on ebay for a few bucks, search "dc-dc converter step up"), and you'd need to either use a level shifter to shift to 5v, or run the chip at 5v.
You are building an electronic device on your own PCB - and you do not know what a regulator is?
Paul__B:
You are building an electronic device on your own PCB - and you do not know what a regulator is?
To be fair, there are boost converters sold as "switching regulators" (not that I condone that nomenclature), but I had a similar reaction. But that really just goes to show how easy it is to design boards and have them produced in this day and age. I usually try to educate people who display such surprising knowledge gaps, instead of making fun of them, but that's just my style.
Well, to be fair, it's half fun and half serious. It seems to be a waste of time to actually "build a board" - if this implies a PCB - if you don't adequately understand the design details and the function of the microcontroller.
And we do get this often - queries as to what is wrong when a PCB has been made and assembled without prototyping.
The most disturbing thing is when someone starts asking details of how to build something that uses the power mains, like a transformerless power supply.
Paul__B:
You are building an electronic device on your own PCB - and you do not know what a regulator is?
Isn't what we call boost or buck converter a switching regulator? If not, then what is a regulator?
Well, I think a boost or buck converter is in fact, just that! And it is in fact the case that EEPROM/ Flash devices contain internal charge pumps - like a MAX233 - in order to develop the necessary voltage to write EEPROM cells (and I would presume these do include a regulator function - someone may clarify that - in order to provide that function correctly).
These are however, somewhat inefficient compared to a switchmode circuit using an external inductor and it would not be really sensible to provide such functionality in a MCU merely to facilitate operation in a particularly narrow set within its operating conditions.
You should presume that the specified operating voltage range for the chip is precisely that - a range of operating voltages over which it will operate (with certain constraints, notably that at lesser voltage, the warranted operating frequency is reduced) whereby it will accept inputs and provide outputs at that operating voltage; nothing more nor less is specified, nor would it be reasonable to expect. A MCU is a MCU and nothing in the specification of a MCU ever implies a voltage regulator!