Hi,
Pxx instead of Mxx means basically that is an early part and the part probably has not qualified for full production. It is normal that you can find Pxxx parts in the first development boards until the device is fully qualified and in full production. The differences between P an M products can vary from one part # to the other. But technically is the same product if they have the same silicon mask version. For example part# with Pxx could have been only tested in a narrow temperature range. So a Pxx part can be exactly the same than Mxxx part but the qualification process could not be complete at the time of manufacturing the part.
I hope this helps.
Luis
