GPIOB->BSRR = 0x01便是把GPIOB port 0升为高电平
GPIOB->BRR = 0x01便是把GPIOB port 0降为低电平GPIOB->BSRR = 0x02便是把GPIOB port 1升为高电平GPIOB->BRR = 0x02便是把GPIOB port 1降为低电平GPIOB->BSRR = 0x04便是把GPIOB port 2升为高电平GPIOB->BRR = 0x04便是把GPIOB port 2降为低电平GPIOB->BSRR = 0x08便是把GPIOB port 3升为高电平GPIOB->BRR = 0x08便是把GPIOB port 3降为低电平
