【正文】 the brownout reset circuit requires an additional 10 – 70 uA of current for operation. The ability to enable or disable the brownout protection to save power consumption is often given, but brownout protection must be enabled 100% of the time to be useful because brownout cannot be predicted. This adds the brownout current consumption directly to the bottom line of the power budget of the system. Pin LeakageLeakage current is sometimes overlooked when choosing a lowpower MCU, but it must be considered for the most demanding lowpower applications. Most lowpower MCUs have specified input leakage currents of 1uA. This could consume up to 20uA for a 20input device! The MSP430 specifies pin leakage currents of 50nA – 1uA max for the same 20input device. Processing EfficiencyFinally, MCU processing efficiency is often misunderstood. It is often thought that 16bit MCUs require twice the memory of 8bit MCUs, but a 16bit architecture can actually require less code than an 8bit architecture and 16bit MCUs usually execute tasks more quickly. For example 8bit MCUs require CPU overhead to manage data in applications that have 10bit A/D conversion data or applications that require 16bit math. SummaryChoosing a lowpower MCU requires investigation beyond datasheet bullet points. But the effort pays off when battery life is extended, or the currentbudget is met.。附錄2Efficient MSP430 Code Synthesis for an FIR FilterABSTRACTDigital filtering can be easily acplished on the MSP430 using efficient multiplication.[1] The tool acpanying this document automatically converts FIR filter coefficients to MSP430 assembly code that can be used in any application. Horner’s method and CSD format is used to acplish the efficient multiply operations. The performance of the filter on the MSP430 is shown by evaluating the gain across all frequencies. Performance in terms of CPU cycles, code size, and frequency response of lowpass, highpass, bandpass, bandstop, and notch filters on the MSP430 is shown in Appendix A. In Appendix C, this application report describes how to pare ultralowpower MCUs. It discusses the key differences between popular lowpower MCUs and how to interpret features and specifications and apply them to application requirements. Contents1 Introduction ............................................................................. .. ........ 22 FIR Filter Code Synthesizer....................................................... ......... 23 References ......................................................................... ....... ....... 4Appendix A FIR Filter Examples .............................. .................. ......... 5Appendix B File List .............................. ....................................... ...... 10Appendix C Choosing An UltralowPower MCU………………..……12List of FiguresA1 LowPass FIR Filter Response .................... .................... ............. 5A2 HighPass FIR Filter Response........................................... ... ..... 6A3 BandPass FIR Filter Response ............................................ ......... 7A4 BandStop FIR Filter Response ............................................ ......... 8A5 Notch FIR Filter Response .................................... ........................ 91 IntroductionAn FIR filter, known for its inherent stability and linear phase property, sometimes is an ideal choice for digital filtering.[2] The filter coefficients are always floating point numbers that need to be scaled to the nearest integer for their operation in fixedpoint machines, such as the MSP430 microcontrollers.[3] In addition, such a filtering in the absence of a hardware multiplier bees expensive in terms of CPU cycles. The solution to both these concerns is Horner’s method. Horner’s method has the ability to perform an integerfloat multiply, thus eliminating the need for scaling of the filter coefficients. The efficiency in terms of CPU cycles is achieved by using only shift and add instructions to perform the multiplication.[1] The tool downloadable with this document generates efficient MSP430 code for any FIR filter, given its coefficients. Additionally, a C wrapper file and data file are generated that perform a frequency sweep of the data to verify the filter39。舉個例子，8位單片機要求在應(yīng)用中CPU在管理數(shù)據(jù)時是處于上級，如10位A/D轉(zhuǎn)換數(shù)據(jù)或者要求16位數(shù)學(xué)的應(yīng)用。 處理效率最后，單片機的處理效率常常被誤解。這樣在一個20引腳輸入的設(shè)備上總消耗將達到20uA。 管腳泄漏選擇一款低功耗單片機時，管腳泄漏電流有時會被忽略，但是在大多數(shù)低功耗要求的應(yīng)用的場合都是必須考慮的。但是失電保護必須100%的時間都在使用中，因為失電是不可預(yù)測的。對大多數(shù)單片機來說，失電保護電路在操作時需要一個額外的1070uA的電流。協(xié)同工作的能力是另一個外設(shè)的關(guān)鍵優(yōu)點。當它不在轉(zhuǎn)換時，它就自動的禁止一些它內(nèi)部的晶振和數(shù)字電路，自動有效的關(guān)閉了自己。它有一種期待的能力，就是個別的設(shè)備可以根據(jù)需要與否而選擇它是否能夠使用，還有更重要的是它可以自動的禁止或者使用這些設(shè)備。一些低功耗單片機僅僅是翻新了2030年沒有為低功耗設(shè)計的體系做外設(shè)。一些外設(shè)，如Timer_A，Timer_B和ADC12為了總體的適應(yīng)性有多種中斷。一款好的低功耗單片機將是有廣泛的中斷能力，為它所有的外設(shè)都提供中斷并且為許多外部的事件提供外部中斷。中斷將CPU從低功耗模式中喚醒，所以單片機有越多的中斷，它就有更強的適應(yīng)性來防止CPU輪流檢測的電流消耗和降低功率消耗。MSP430單片機為CPU提供了一個穩(wěn)定高速的時鐘，一般小于6微秒(通常更快)，同樣執(zhí)行25條指令僅僅需要9us(6us喚醒+)，和信息高速即時的連續(xù)傳遞以及即時的計時準確的時鐘源的訪問。一些單片機提供一種兩階段時鐘喚醒模式，當高頻率時鐘趨于穩(wěn)定的過程中給CPU提供一個低頻率時鐘(通常是32768Hz)，這個過程通常占用1ms或者更長時間。大多數(shù)低功耗單片機都為CPU準備了一個時間小于1020us的“瞬子”時鐘。應(yīng)用程序可能在一秒鐘進入和退出各種低功耗模式幾次或者上百次。類似的外圍設(shè)備有可能還處于活動狀態(tài)，但是如果沒有的話，包括了RAM的數(shù)據(jù)保持。LPM3通常被稱為實時時鐘模式，因為這種模式允許定時器以32768Hz的低功耗時鐘源進行操作，電流消耗1uA，周期性喚醒系統(tǒng)處于激活狀態(tài)。模式LPM1和LPM2將各種時鐘功能添加到禁用列表中。舉個例子，MSP430單片機提供5種低功耗模式。 低功耗模式低功耗模式是單片機能夠滿足電流預(yù)算中的一種重要特征。 平均電流消耗在低功耗設(shè)計中，平均電流消耗決定了電池的壽命。大多數(shù)MCU芯片供應(yīng)商都提供低功耗芯片，但是選擇一款適合你的應(yīng)用場合通常比較困難。這個文件是模擬頻率掃描數(shù)據(jù)文件。這個文件是模擬頻率掃描數(shù)據(jù)文件。這個文件是模擬頻率掃描數(shù)據(jù)文件。這個文件是模擬頻率掃描數(shù)據(jù)文件。這個文件是模擬頻率掃描數(shù)據(jù)文件。用戶可以寫入各種參數(shù)和得到每種頻率的值，并且在I/O終端上看到濾波器的頻率響應(yīng)。它必須存放在和C包文件和MSP430匯編文件的同一個目錄下來估計頻率響應(yīng)。這個文件一共包含了17600個整型采樣數(shù)據(jù)，范圍從2047到+2047。這是個MSP430匯編代碼文件。這個壓縮文件中還包括了一個采樣文件，用戶可以在這個文件上面自己設(shè)定系數(shù)。這個文件必須和代碼合成器在同一個目錄下。每一個例子中包含的文件都放在各自獨立的目錄下。在得到的規(guī)范化的對數(shù)刻度上的劃分與設(shè)計規(guī)范的頻率相一致。在得到的規(guī)范化的對數(shù)刻度上的劃分與設(shè)計規(guī)范