Bound to be a simple explanation, but...

I saved the following screenshot from a post here recently. Just noticed it shows the chip has 30 pins, not 28 as all mine have. But darned if I can find the post again now to resolve the contradiction.

 

hi Terry,
It is a 32pin Package.
E
https://www.google.com/search?q=atm...iAhVqSxUIHdUdB3IQsAR6BAgFEAE&biw=1619&bih=916

 

hi Terry,
It is a 32pin Package.
E
https://www.google.com/search?q=atm...iAhVqSxUIHdUdB3IQsAR6BAgFEAE&biw=1619&bih=916

View attachment 179211

View attachment 179212

Thanks Eric, but that screenshot you’ve shown seems to be an ATMEGA328, not an ATMEGA328P-U?

 

hi T,
It is obviously a 32 pin package in that first drawing you posted, so I would look for the pins on the 32 device that are not present on the 28 version.
Often its the power and ground pins.
E

 

Thanks Eric, but that screenshot you’ve shown seems to be an ATMEGA328, not an ATMEGA328P-U?

Hi Eric: My puzzlement is that I’ve always assumed an IC’s full number, with any prefixes or suffixes, defines it uniquely, including pin numbering. Is that untrue?

 

hi Terry,
After much searching and comparing I have come to the conclusion, whoever drew that initial drawing misnamed the ATmega 328-PU, which in fact a 28 pin.
E

 

Thanks Eric, much appreciate your taking the trouble to solve that mystery.

Also pleased it's not just my ignorance!

 

My apologies, My first design used the DIP package but I switch to a smaller smd package after awhile and did not think to change the label.

Its all in the datasheet to correct the pin out for your application.
https://www.mouser.com/datasheet/2/...AVR-Microcontroller-ATmega48A-48P-1315288.pdf



Here, is the old version for 28pin:

 

Thanks narkeleptk.