ATmega164P/324P/644P系列过去的型号都停产了，目前都是新型号ATmega164PA/324PA/644PA系列来替代。以下是官方提供的相关区别说明：
1 Introduction
In order to optimize the manufacturing process and to further reduce current consumption, an optimized version of ATmega164P/324P/644P has been introduced.

The ATmega164PA/324PA/644PA is a functionally identical, drop-in replacement for the ATmega164P/324P/644P. All devices are subject to the same qualification process and same set of production tests, but as the manufacturing process is not the same some electrical characteristics differ.

ATmega164P/324P/644P and ATmega164PA/324PA/644PA have separate datasheets. This application note outlines the differences between the two devices and the datasheets. There is also a detailed change log to assist the user at the end of the ATmega164PA/324PA/644PA datasheet. Remember to always use the latest revision of the device datasheet.

Minor differences in typical characteristics are not discussed in this document as long as the low and high limits remain the same. For detailed information about the typical characteristics, see sections “Electrical Characteristics” and “Typical Characteristics” of the device datasheets.

Note: This application note serves as a guide to ease migration. For complete device details, always refer to the most recent version of the ATmega164PA/324PA/644PA datasheet.

2 Changes in Characteristics
This section outlines major differences in characteristics that may have an effect on the application in which the device is used. For detailed information, refer to the most recent version of the device datasheets.

2.1 Current Consumption
Active and Idle mode current consumption of the device has been reduced significantly. The tables below present typical current consumption figures at room temperature. All values are taken from device datasheets, unless otherwise noted.

3 Signature Bytes
The table below summarizes the difference between the signature bytes of ATmega324P and ATmega324PA. Note, that no change for ATmega164P/644P and ATmega164PA/644PA.

4 Datasheet Changes
For a summary of changes, see the datasheet revision history at the end of the ATmega164PA/324PA/644PA datasheet.