嵌入式系统设计考试模拟题

嵌入式系统设计考试模拟题c//单总线延时函数（需根据系统时钟校准）voidDS18B20_Delay(uint16_tus){/*软件延时或定时器实现（例：STM32定时器延时）*/}//复位脉冲发送uint8_tDS18B20_Reset(void){uint8_tack=0;GPIO_ResetBits(DQ_GPIO,DQ_PIN);//拉低DQDS18B20_Delay(480);//保持480μs（复位脉冲）GPIO_SetBits(DQ_GPIO,DQ_PIN);//释放总线DS18B20_Delay(60);//等待从设备应答（60μs）ack=GPIO_ReadInputDataBit(DQ_GPIO,DQ_PIN);//读取应答位DS18B20_Delay(420);//等待复位结束（420μs）returnack;}//写位操作voidDS18B20_WriteBit(uint8_tbit){GPIO_ResetBits(DQ_GPIO,DQ_PIN);DS18B20_Delay(2);//拉低后立即写（2μs）if(bit)GPIO_SetBits(DQ_GPIO,DQ_PIN);DS18B20_Delay(60);//保持60μs（满足位时间要求）GPIO_SetBits(DQ_GPIO,DQ_PIN);}//读位操作uint8_tDS18B20_ReadBit(void){uint8_tbit=0;GPIO_ResetBits(DQ_GPIO,DQ_PIN);DS18B20_Delay(2);//拉低2μsGPIO_SetBits(DQ_GPIO,DQ_PIN);DS18B20_Delay(8);//等待数据稳定（8μs）bit=GPIO_ReadInputDataBit(DQ_GPIO,DQ_PIN);DS18B20_Delay(50);//保持剩余时间（50μs）returnbit;}//读字节uint8_tDS18B20_ReadByte(void){uint8_ti,byte=0;for(i=0;i<8;i++){byte|=(DS18B20_ReadBit()<<i);//按位读取}returnbyte;}//写字节voidDS18B20_WriteByte(uint8_tbyte){uint8_ti;for(i=0;i<8;i++){DS18B20_WriteBit((byte>>i)&0x01);//按位写入}}//读取温度（含CRC校验，需实现CRC算法）floatDS18B20_ReadTemp(void){uint8_ttemp_l,temp_h;uint16_ttemp_raw;floattemp;if(DS18B20_Reset()==1)return-127.0;//复位失败DS18B20_WriteByte(0xCC);//跳过ROM（单设备场景）DS18B20_WriteByte(0x44);//启动温度转换DS18B20_Delay(750);