Introduction to Microcontrollers

More documents

Recommendations

Info

12 CHAPTER 2. MICROCONTROLLER COMPONENTS Arithmetic Logic Unit At the core of the CPU is the arithmetic logic unit (ALU), which is used to perform computations (AND, ADD, INC, . . . ). Several control lines select which operation the ALU should perform on the input data. The ALU takes two inputs and returns the result of the operation as its output. Source and destination are taken from registers or from memory. In addition, the ALU stores some information about the nature of the result in the status register (also called condition code register): Z (Zero): The result of the operation is zero. N (Negative): The result of the operation is negative, that is, the most significant bit (msb) of the result is set (1). O (Overflow): The operation produced an overflow, that is, there was a change of sign in a two’scomplement operation. C (Carry): The operation produced a carry. Two’s complement Since computers only use 0 and 1 to represent numbers, the question arose how to represent negative integer numbers. The basic idea here is to invert all bits of a positive integer to get the corresponding negative integer (this would be the one’s complement). But this method has the slight drawback that zero is represented twice (all bits 0 and all bits 1). Therefore, a better way is to represent negative numbers by inverting the positive number and adding 1. For +1 and a 4-bit representation, this leads to: For zero, we obtain 1 = 0001 → −1 = 1110 + 1 = 1111. 0 = 0000 → −0 = 1111 + 1 = 0000, so there is only one representation for zero now. This method of representation is called the two’s complement and is used in microcontrollers. With n bits it represents values within [−2 n−1 , 2 n−1 − 1]. Register File The register file contains the working registers of the CPU. It may either consist of a set of general purpose registers (generally 16–32, but there can also be more), each of which can be the source or destination of an operation, or it consists of some dedicated registers. Dedicated registers are e.g. an accumulator, which is used for arithmetic/logic operations, or an index register, which is used for some addressing modes. In any case, the CPU can take the operands for the ALU from the file, and it can store the operation’s result back to the register file. Alternatively, operands/result can come from/be stored to the memory. However, memory access is much slower than access to the register file, so it is usually wise to use the register file if possible.
2.1. PROCESSOR CORE 13 Example: Use of Status Register The status register is very useful for a number of things, e.g., for adding or subtracting numbers that exceed the CPU word length. The CPU offers operations which make use of the carry flag, like ADDC a (add with carry). Consider for example the operation 0x01f0 + 0x0220 on an 8-bit CPU b c : CLC ; clear carry flag LD R0, #0xf0 ; load first low byte into register R0 ADDC R0, #0x20 ; add 2nd low byte with carry (carry
Page 1 and 2: Introduction to Microcontrollers Co
Page 3 and 4: 2.7.2 Power Consumption and Sleep .
Page 6 and 7: Preface This text has been develope
Page 8 and 9: 2 CHAPTER 1. MICROCONTROLLER BASICS
Page 16 and 17: 10 CHAPTER 1. MICROCONTROLLER BASIC
Page 20 and 21: 14 CHAPTER 2. MICROCONTROLLER COMPO
Page 68 and 69:
62 CHAPTER 2. MICROCONTROLLER COMPO
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
74 CHAPTER 3. COMMUNICATION INTERFA
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
90 CHAPTER 4. SOFTWARE DEVELOPMENT
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
130 CHAPTER 5. HARDWARE A somewhat
Page 138 and 139:
132 CHAPTER 5. HARDWARE This effect
Page 140 and 141:
134 CHAPTER 5. HARDWARE B A (a) A B
Page 142 and 143:
136 CHAPTER 5. HARDWARE e a f g d F
Page 144 and 145:
138 CHAPTER 5. HARDWARE new value f
Page 146 and 147:
140 CHAPTER 5. HARDWARE Relays come
Page 148 and 149:
142 CHAPTER 5. HARDWARE N S N S Fig
Page 150 and 151:
144 CHAPTER 5. HARDWARE motor speed
Page 152 and 153:
146 CHAPTER 5. HARDWARE A B UM moto
Page 154 and 155:
148 CHAPTER 5. HARDWARE requires a
Page 156 and 157:
150 CHAPTER 5. HARDWARE Half- and m
Page 158 and 159:
152 CHAPTER 5. HARDWARE Stepper Mot
Page 160 and 161:
154 CHAPTER 5. HARDWARE
Page 162 and 163:
156 APPENDIX A. TABLE OF ACRONYMS E
Page 164 and 165:
158 APPENDIX A. TABLE OF ACRONYMS T
Page 166 and 167:
160 INDEX Ankerspule (armature coil
Page 168 and 169:
162 INDEX Embedded Processor, 7 Emb
Page 170 and 171:
164 INDEX non-volatile RAM, 29 NVRA
Page 172 and 173:
166 INDEX source input, 38 source o
Page 174 and 175:
168 INDEX
show all

Introduction to Microcontrollers

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?