【正文】 數(shù) 值 寄存器（在 R15的例子）。在這個例子中，我們檢查有效范圍以外的兩端的條件。multiply R15 by two,since PC is always even Rla R15 。range checking Jge outofrange 。一個例外的規(guī)則是，當(dāng)代碼跳轉(zhuǎn)到一個地方的執(zhí)行情況，使用一個開關(guān)使其依賴于一個給定值。一代基于 W(S)中有一定的應(yīng)用價值 ,并描述指令字由下列表格。 常數(shù)發(fā)生器 R3功能為常數(shù) ,R2 發(fā)電機(jī) ,所以寄存器模式可以用來代替直接模式為一些常見的常數(shù)。 不幸的是，我不 知道今天的 R8， R9 和 R15 代表什么價值。了解您的 工具。為了效率目的任何經(jīng)常使用的變量需要存放在這些地址之一。 工作寄存器 該 39。430 處理器包括一個相當(dāng)標(biāo)準(zhǔn)的 ALU（算術(shù)邏輯單元）。這是非常靈活，它的尋址方式更復(fù)雜比大多數(shù)其他小型處理器。 第二，有大量的工作寄存器。 所有的存儲器，包括 RAM，ROM中，信息存儲，特殊功能寄存器和外設(shè)寄存器映射到一個單一的， 連續(xù)的地址空間。 39。 有 共同特征的沒有一貫表現(xiàn)（ ADC 的類型，定時器編號等），并有其他一些不一致的 地方（例如， 33 系列有乘法器，但 13 和 43 沒有）。4xx裝置 。1 xx， 帶有 LCD 驅(qū)動器內(nèi)置。430 是競爭在價格與 8 位控制器市場，同時支持 8位和 16 位 指令，通過大多數(shù)同樣大小的平臺進(jìn)位。 該 這本書的目的是介紹一些最常用的信息 ，通過一些有用的建議和經(jīng)驗(yàn)法則。 我 假定讀者對微控制器基礎(chǔ)設(shè)計(jì)無論是專業(yè)或?qū)W術(shù)上有一定的經(jīng)驗(yàn)。Restore previous value to R12 Reti 。We will use R12 Mov P1IN,R12 。 Rla R15 。put the switch value into R15 Cmp R15,8 。430 gives the developer twelve 16bit working registers, R4 through R15. (R0 through R3 are used for other functions, as described later.) They are used for register mode operations (see Addressing Modes, Chapter 8), which are much more efficient than operations which require memory access. Some guidelines for their use: Use these registers as much as possible. Any variable which is accessed often should reside in one of these locations, for the sake of efficiency. Generally speaking, you may select any of these registers for any purpose, either data or address. However, some development tools will reserve R4 and R5 for debug information. Different pilers will use these registers in different fashions, as well. Understand your tools. Be consistent about use of the working registers. Clearly document their use. I have code, written about 8 months ago, that performs extensive operations on R8, R9, and R15. Unfortunately, I don39。3xx, and 39。中文 5030 字 Embedded Systems Design using the TI MSP430 Series（ selection） This book is intended for the embedded engineer who is new to the field, and as an introduction and reference for those experienced with microcontroller development, but are new to the MSP430 family of devices. I have assumed that the reader has some experience with microcontrollerbased design, either professionally or academically. As an example, the book de scribes interrupt functionality in detail, but assumes that you, the reader, already know what an interrupt is and how to use it. It is also important to note that, while much of the information in this book is identical to that which is available from the TI documentation, this book is intended to supplement, not replace that valuable source of information. The Users Guides and Application Notes together offer a depth and breadth of technical information that would be difficult to replicate in a single source. The intent of this book is to highlight some of the most monly used information, along with some helpful suggestions and rules of thumb. The MSP430 Family The MSP430 family is a broad family of low power, feature rich 16bit microcontrollers from Texas Instruments. They share a mon, RISCtype, Neumann CPU core. The 39。1xx, 39。430 processor includes a pretty typical ALU (arithmetic logic unit). The ALU handles addition, subtraction, parison and logical (AND, OR, XOR) operations. ALU operations can affect the overflow, zero, negative, and carry flags. The hardware multiplier, which is not available in all devices, is implemented as a peripheral device, and is not part of the ALU (see Chapter 6). Working Registers The 39。t let this happen to you. No matter how obvious or trivial register use seems, document it anyway. Constant Generators R2 and R3 function as constant generators, so that register mode ma y be used instead of immediate mode for some mon constants. (R2 is a dual use register. It serves as the Status Register, as well.) Generated constants include some mon singlebit values (0001h, 0002h, 0004h, and 0008h), zero (0000h), and an all 1s field (0FFFFh). Generation is based on the W(S) value in the instruction word, and is described by the table below. W(S) value in R2 value in R3 00 ———— 0000h 01 (0) (absolute mode) 0001h 10 0004h 0002h 11 0008h 0FFFFh Program Counter The Program Counter is located in R0. Since individual memory location addresses are 8bit, but all instructions are 16 bit, the PC is constrained to even numbers (. the LSB of the PC is always zero). Generally speaking, it is best to avoid direct manipulation of the PC. One exception to this rule of thumb is the implementation of a switch, where the code jumps to a spot, dependent on a given value. (., if value=0, jump to location0, if value=1, jump to location1, etc.) This process is shown in Example . Example Switch Statement via Manual PC Control Mov value,R15 。more range checking Jn outofrange 。PC goes to proper jump Jmp value0 Jmp value1 Jmp value2 Jmp value3 Jmp value4 Jmp value5 Jmp value6 Jmp value7 Outofrange Jmp RangeError This is a relatively mon approach, and most C pilers will implement switch statements with something similar. When implementing this manually (., in assembly language), the programmer needs to keep several things in mind: Always do proper range checking. In the example, we checked for conditions outside both ends of the valid range. If this is not performed correctly, the code can jump to an unintended location. Pay close attention to the addressing modes of the jump statements. The second doubling of R15, prior to the add st