说明：  AVR单片机入门及C语言高效设计实践（四） ATMEAG16L的I／O端口特点及使用 ATMEAG16L单片机有32个通用I／O口，分为PA、PB、PC和PD四组，每组都是8位。这些I／O口都可以通过各自的端口寄存器设置成输入和输出（即作为普通端口使用），有些I／O口还具有第二功能（我们在后面使用到这些第二功能时再介绍）。
(AVR C language portal and efficient design practice (4) ATMEAG16L the I/O Ports characteristics and use of a microcontroller ATMEAG16L 32 common I/O mouth into PA, PB, PC and PD four groups, each group are eight. These I/O I can through their respective ports Register set to input and output (that is, use as a general port), Some I/O I also have the second function (in the back of the use of these second function tell).)