Introduction - If you have any usage issues, please Google them yourself
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.