已知Serial.available()函数用于判断串口中是否有内容;Serial.read()函数用于读串口中的内容,在用户敲了'O‘键以后,以下程序运行的效果为? int ledpin = 13; int val = 'O'; void setup(){ Serial.begin(9600); pinMode(6, OUTPUT); } void loop(){ if( Serial.available() ){ val = Serial.read(); if( val == 'O' ){ digitalWrite(6, HIGH); } else if( val == 'F' ){ digitalWrite(6, LOW); } else{ digitalWrite(6, HIGH); delay(1000); digitalWrite(6, LOW); delay(1000); } } }