描述下列后面带有*****语句的作用。 u16 scankb(u16 showdata) { u16 ledkbdata=0; u16 keytag=0x0010; delay_ms(30); while(keytag<0x0100) { Led_Set(showdata | keytag); ledkbdata=(((~Led_Readdata()) | keytag)<<8) | 0x00f0; if((ledkbdata & 0x0f00)!=0x0000 )break; //***** keytag=keytag<<1; } while((Led_Readdata() & 0x000f)!=0x000f); Led_Set(ledkbdata); delay_ms(30); return ledkbdata; }