【正文】 rature data in the form of multiple 1s and 0s are passed to the microcontroller, often via a serial bus. Along the same bus, data are sent to the temperature sensor from the microcontroller, usually to set the temperature limit at which the alert pin39。C or 176。C parts provide an offset so that negative temperatures can be monitored using a singleended supply. In most applications, the output of these devices is fed into a parator or an A/D converter to convert the temperature data into a digital format. Despite the need for these additional devices, thermistors and silicon temperature sensors continue to enjoy popularity due to low cost and convenience of use in many situations. Digital I/O Temperature Sensors About five years ago, a new type of temperature sensor was introduced. These devices include a digital interface that permits munication with a microcontroller. The interface is usually an I2C or SMBus serial bus, but other serial interfaces such as SPI are mon. In addition to reporting temperature readings to the microcontroller, the interface also receives instructions from the microcontroller. Those instructions are often temperature limits, which, if exceeded, activate a digital signal on the temperature sensor IC that interrupts the microcontroller. The microcontroller is then able to adjust fan speed or back off the speed of a microprocessor, for example, to keep temperature under control. This type of device is available with a wide variety of features, among them, remote temperature sensing. To enable remote sensing, most highperformance CPUs include an onchip transistor that provides a voltage analog of the temperature. Only one of the transistor39。s onchip pn junction. Another important feature found on some of these types of sensors including the sensor shown in Figure 3 is the ability to interrupt a microcontroller when the measured temperature falls outside a range bounded by high and low limits. On other sensors, an interrupt is generated when the measured temperature exceeds either a high or a low temperature threshold ., not both . For the sensor in Figure 3, those limits are transmitted to the temperature sensor via the SMBus interface. If the temperature moves above or below the circumscribed range, the alert signal interrupts the processor. Pictured in Figure 4 is a similar device. Instead of monitoring one pn junction, however, it monitors four junctions and its own internal temperature. Because im39。s reliability: at the motherboard which is essentially the ambient temperature inside the chassis , inside the CPU die, and at other heatgenerating ponents such as graphics accelerators and harddisk drives. Battery packs incorporate temperature sensors for safety reasons and to optimize charging profiles, which imizes battery life. There are two good reasons for monitoring the temperature of a harddisk drive, which depends primarily on the speed of the spindle motor and the ambient temperature: The read errors in a drive increase at temperature extremes, and a hard disk39。s internal counter measuring time, the signals from this type of temperature sensor are readily transformed to a measure of temperature. The sensor in Figure 7 outputs a square wave whose frequency is proportional to the ambient temperature in Kelvin. The device in Figure 8 is similar, but the period of the square wave is proportional