DS1670便携式系统控制器-DS1670 Portable

文章摘要：Power to the SRAMs is provided from the VCCO pin of the DS1670. When VCC is within nominal limits (greater than 2.7 volts typical), VCCO is internally connected to VCC. However, when VCC goes below nominal limits, VCCO is internally connected to VBAT, thus ensuring that the SRAM data is maintained i

DS1670便携式系统控制器-DS1670 Portable,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com

Power to the SRAMs is provided from the VCCO pin of the DS1670. When VCC is within nominal limits (greater than 2.7 volts typical), VCCO is internally connected to VCC. However, when VCC goes below nominal limits, VCCO is internally connected to VBAT, thus ensuring that the SRAM data is maintained in the event of a primary power supply failure. VBAT is typically connected to a lithium battery, rechargeable battery, or super capacitor. Figure 3 illustrates VBAT connected to a super capacitor. The super capacitor is charged whenever the power source connected to VCC is a diode drop above VBAT plus the voltage drop across resistor R1. R1 is used to decrease the charge current to the super capacitor. Note that in this application, the primary power source connected to VCC is a battery. This could be a rechargeable battery pack or perhaps a series of AA cells. Regardless of the type of battery used, the DS1670 allows the battery to be changed without the loss of important data. Depending on the size and type of super capacitor or battery connected to VBAT, the data will be saved from several hours to several years without replacing the main system battery. It should be noted also that when using a super capacitor, the limiting factor is often the internal leakage of the capacitor itself. In other words, the battery back-up current consumed by the DS1670 and SRAMs is negligible compared to the internal leakage of the capacitor.

Microprocessor Monitoring

The illustrated typical application also takes advantage of the microprocessor monitoring features of the DS1670. The active-low RST of the DS1670 is connected to the active-low RESET pin of the microprocessor. The DS1670 will generate a reset signal if VCC goes out of the nominal limits or if the watchdog timer is allowed to expire. Toggling the strobe (active-low ST) input before the watchdog timer expires will keep the watchdog from generating a reset. The watchdog timer can be disabled or programmed by the user to be 250ms, 500ms, or 1000ms. It is also possible to connect the active-low RST pin to a monetary pushbutton switch to allow a manual reset of the system. In this type of application the active-low RST pin will produce a 250ms active reset after being momentarily grounded by an external momentary switch.

Real Time Clock

Another important feature of the DS1670 is the Real Time Clock (RTC). The RTC provides the system with seconds, minutes, hours, day, date, month, and year information. The accuracy of the clock is typically ±1 minute per month at room temperature. An especially powerful function of the RTC is the alarm. The alarm gives the user flexibility to program events at a specific time of the day. The DS1670 can be programmed to generate a single alarm or, through the use of its alarm mask bits, can generate an alarm once every second, minute, hour, or day. Added flexibility is provided in that the alarm is functional both when the device is powered by VCC or when powered by VBAT. Generating an alarm while powered by VBAT is especially useful because this allows the DS1670 to "wake up" a sleeping system. For example, a portable data logger may need to collect data once every hour. This system could be placed in a low power "sleep mode" when idle. The alarm could be used to "wake up" the system at the appropriate time to collect data. After the collection is completed, software could place the system back into sleep mode where it would remain until the next alarm interrupt.

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Tag:控制技术，计算机控制技术,工厂电气控制技术，控制技术