ATmega48/88/168的PB5是SPI时钟输出，接74HC595/74HC165的移位时钟输入端；PB4是SPI的MISO数据输人，接74HC165的数据输出；PB3是SPI的MOSI数据输出，接74HC595的串行数据输入端SER；PB2接74HC595/74HC165的锁存时钟输入端。-PB5 The ATmega48/88/168 SPI clock output connected to the input end of a 74HC595/74HC165 the shift clock　PB4 SPI MISO data input, then 74HC165 data output　PB3 SPI MOSI data output, then 74HC595 string The line data input terminal SER　PB2 a latch clock input terminal connected 74HC595/74HC165.