Atmega644p or atmega644a on V1.2 motherboard?

I ordered a V1.2 motherboard from makerbot.com and I'm following the instructions for building it on the wiki, but the wiki says to use a Atmega644p while on the printed circuit board I bought it says 644a next to where the atmega goes on the board. I just need to know which one I should use.

Also I know there are newer electronics but I'm an electrical engineering student and the $500 I have spent on this project has already taught me more than any $1500 dollar class and I wanted to use the old electronics so I could build them all from PCB's and have more individual components to build and play with.

Thanks in advance.

Check the data sheets for the two chips, and make sure they are pin compatible, I believe the difference is that the 644p is a low power version of the 644A.

The ATmega 644P is less power hungry - 0.25 Watts instead of 0.5 Watts or so. It also has an additional serial port (UART1) and a different signature. For the later, things like #ifdef __AVR_ATmega_644P__ don't work for the 644 (needs #ifdef __AVR_ATmega_644__) and may require some adjustments in the firmware.

So - unless you're willing to fix a few minor things, I'd purchase the 644P. Two or three dollars more for less hassle.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY