各位高手，小弟正在基于AVR单片机开发一款智能小车，遇到“LCD无法显示速度数据”，调试了一下，屏蔽了大部分代码保留了对LCD操作的代码，当执行到“LCD_RS_PORT&=~LCD_RS;”这一句时，测量了RS管脚的电平，发现RS管脚电平并未拉低，仍然为高电平。请教其中的原因。谢谢。部分代码如下：
void LCD_init(void)        
{
 LCD_DATA_DDR|=LCD_DATA;  
 LCD_EN_DDR|=LCD_EN;      
 LCD_RS_DDR|=LCD_RS;      
 LCD_RW_DDR|=LCD_RW;      
 LCD_RW_PORT&=~LCD_RW;        //RW=0
 LCD_write_command(0x28);
 
 #if 0
 LCD_en_write();
 delay_nus(40);
 LCD_write_command(0x28);  
 LCD_write_command(0x0c);  
 LCD_write_command(0x01);  
 delay_nms(2);
 #endif
}
void init_devices(void)
{
   //stop errant interrupts until set up
   CLI(); //disable all interrupts
   port_init();
   timer0_init();
   LCD_init();
   time1_init();
time2_init();
INT_init();
   
   TIMSK |= BIT(2);
TIMSK |= BIT(0);
TIMSK |= BIT(6);

SEI(); //re-enable interrupts
//all peripherals are now initialized
}
void main(void)
{
   int counter = 0;
int i;
int stop_count = 0;

//MCUCSR &= ~BIT(4);
MCUCSR |= BIT(7);
MCUCSR |= BIT(7);

//vInitEeprom();
uart0_init();
   init_devices();
   //EECR |= BIT(EERIE);
DUTY1=50;
   DUTY2=50;
   addr = 1;

while (1)
{
   delay_ms (10);
}
}