I have confusion about the chip on the Arduino R3 as seen on the web site. the confusion is with in the chip and its pin outs. the chip on my board is the ATMEGA328P U. Now the schematic on the Arduino website shows the ATMEGA328P-PU now is this the same chip I have ? Also why is the pin outs different then the data sheet I found on mouser for the ATMEGA328-PU (photo below) ? If i buy the one on mouser the ATMEGA328-PU is this the same chip as on my board ?
Also to add to my post the chip on the board i have is the same one as in the product photo on the website. ATMEGA328P U. I'm just confused as to why the data sheet on mouser.com in photo (I attached) shows different pin outs then what the schematic on the Arduino website shows for pin outs for the chip. The chip is listed as the ATMEGA328-PU on mousers website and that's the pin outs of the data sheet I posted .
Atmega328P-PU is not the same as Atmega328-PU.
They have different signature bytes. The IDE does not recognize the 2nd part.
Atmega328P-PU and Atmega328P-U are likely the same chip, just different ages.
https://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061B.pdf
If you add the Minicore to the IDE
then all the 328 variants can be used without issues.
The 328P is PicoPower, draws less current per the datasheet ((probably not easily measurable).
-AU parts are the leaded surface mount parts.
-MA parts are the smaller lead-less surface mount parts.
Ok that helps but the another question I have is I'm trying to make a stand alone PCB using Eagle. I was trying to find the exact chip that my board has. The chip on my board is is listed as ATMEGA328P U there is no dash. The one i was looking at on mouser.com is the same data sheet u just posted as far as pin outs and is listed as ATMEGA328-PU. So I was trying to make sure before I design it I is the same chip that's in my board along with the same pin configuration also when i use the footprint in eagles its correct. So I'm lost between what the schematic shows for pin outs on the Arduino website and the pin outs the data sheet shows on mouser.com for the ATMEGA328-PU.
The schematic rarely shows the physical pin out. The pins are often rearranges to make it easier to draw. The best source of the pinout is the data sheet, which @crossroads has shown. Second best are CAD library items in PCB design packages which you should, anyway, always check against the data sheet.
Ensure that you get exactly the right part number: ATMEGA328P-PU otherwise you have difficulty with some Arduino cores.
@crossed with the OP
My Eagle has Mega8-P, I just right-click and give it the value Atmega328P-PU so when a Parts List is Exported, it lists the correct part.
All 328s will be the same (328, 328P, -P, -PU, -U), 328PB is a different part tho with somewhat different features.
I haven't found anything saying what the difference is between -PU and -PN, except -PN costs a little more at Mouser.
Your Arduino Uno should have shipped with 328P-PU if it is a real Arduino board. Chinese variants, all bets are off.
Download the Uno Eagle files and check out what they have.
https://content.arduino.cc/assets/UNO-TH_Rev3e-reference.zip
So if I'm understanding this correctly what @ cross roads just posted is the ATMEGA328P-PU chip just in eagles and set up so its easy to read in schematic view. But when I go to the footprint view it seems to be the same configuration as the data sheet pin line up. So the difference is that like you said @6v6gt they just lay it out like that in schematic view to make it easy to read if I'm understanding that correctly ? So what @Crossroads posted is the same as the schematic on the Arduino site as far as pin outs. But in footprint view thing it looks like the data sheet. But when they go to print it at the factory using the parts list they will match it to the data sheet and lay it out like it is in the footprint view?
Also as far as my chip mine is labeled ATMEGA328P U just like the photo below.
So I'm guessing that's the ATMEGAP-PU chip its just not listed that way on the board or something ?
Here is the Arduino Uno Schematic: https://content.arduino.cc/assets/UNO-TH_Rev3e_sch.pdf
The part number there is usually the definitive one. In this case, ATMEGA328P-PU is the item thing to order. That it doesn't correspond 100% with what is printed on the chip itself is, in this case, not relevant. For you, important is that the chip (based on its signature) is recognised by the IDE.
With the foot print, you should check that the pin numbering corresponds with that in the data sheet. For a 28 pin DIP package, as in the case of theATMEGA328P-PU, that is not usually a problem.
If your designing a PCB, just post your final design here for review.
Ok thank you so much so I do need to get the ATMEGAP-PU its just the labeling is different on the chip got you. Also get the with the corresponding eagle file for the ATMEGAP_PU. I will be sure to post the design for review here. I now see the difference between the schematic view and the board view schematic just easy to look at the board view is how it will actually be printed.
THANK YOU guys for the help and clearing up a lot of the confusion I was having. 
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