On my Arduino UNO the chip part number is ATMEGA328P-U, i recently bought a ATMEGA328-PU to make a standalone Arduino. realized the part number differences after receiving the package...

I noticed that some arduino UNOs have the chip with part number of ATMEGA328P-PU! I'm totally confused!

Those chip are the same? can i use the one that i bought for an standalone Arduino?

If no what are the differences?


The main difference is the bit before the -. That is, the 328 vs the 328P. The "P" there denotes "Picopower" which allows the chip to run at very low power consumptions.

Basically the P version is a more modern version of the non-P chip. There are probably other internal differences too but you will have to check the datasheets thoroughly for those.

Everything after the - is to do with the packaging and environmental grading of the chip. For example PU is a -40C to +85C grade DIP chip. ANR is a -40C to +105C grade TQFP chip, etc.

If you see 328P-U then that's probably a fake chip. There's no such thing as single U suffix.

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There are three die types:




all have different signature bytes which may or may not impact loading code into them. Generally tho the programming software needs to know which part type is being used, at a minimum for installing bootloader code. Serial downloading may end up ignoring the signature bytes of a bootloaded part.

They can be had in different packaging, this is what Digikey is showing as available options:

-PU - 28 pin DIP

-AU - 32 pin TQFP

-AN - 32 pin TQFP

-MM - 28 pin leadless package, smaller than 32 pin leadless

-MN - 32 pin leadless package

-MU - 32 pin leadless package

-15AZ - 32 pin TQFP, rated for a higher temperature range

-15MZ - 32 pin leadless package rated for a higher temperature range

Any letters to the right of those seen when ordering indicate the method they are supplied - loose parts, parts in a reel, parts in a tube, etc.

Anything else is either an older part that did not follow the convention, or is a counterfeit part.

Tables 38.7 and 38.8 lists these options for the 328 and 328P for example, with H indicating a type of lead finish, and R indicating Tape & Reel availability:









And 328P options:








With these rated to 105C






I think you need to pull up the Automotive data sheet to see the Z numbered parts.

And the PB is a different data sheet as well.

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  • That help a lot, but in case other people are finding this looking for ATmegaXX-XXPI, then: PI are 40-pin, PDIP – rasmusm Nov 24 '19 at 19:19
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    '328s are never 40-pin. There are 40-pin DIPs in the Atmega family, and some, like the '644, '1284P, have been brought into the Arduino IDE. I like the '1284P myself; 32 IO arranged as 4 8-bit ports, dual hardware serial, 128K flash, 16K SRAM (twice what the '2560 has). – CrossRoads Dec 9 '19 at 3:17
  • Good point and my comment was more general for ATmega's, as this is the first google hit and your answer are a good reference, so i just wanted to add the answer to my own question there was about ATmega16-16pi, just in case it could help somebody else finding this looking for that. – rasmusm Dec 9 '19 at 11:31

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