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The Watchdog Timer
9-2
9.1 The Watchdog Timer
The primary function of the watchdog-timer module (WDT) is to perform a
controlled-system restart after a software problem occurs. If the selected time
interval expires, a system reset is generated. If the watchdog function is not
needed in an application, the module can work as an interval timer, to generate
an interrupt after the selected time interval. The WDT diagram is shown in
Figure 9–1.
Figure 9–1. Schematic of Watchdog Timer
IS0
SSEL
HOLD
NMIES
16b
Counter
Clear
4
A
B
CLK
NMI
TMSEL
CNTCL
IS1
SMCLK
ACLK
Watchdog Timer
Control Register
16
MDB
LSB
MSB
1
1
A
Q6
Q9
Q13
Q15
3
2
1
(Asyn)
EN
Write Enable
Low Byte
Password
Cmp.
EQU
R/W
PUC
0
1
0
1
1
0
1
0
WDTCTL
Y
Int.
Flag
EQU
WDTQn
See Interrupt
Definition
PUC
WDTCNT
Pulse
Generator
Features of the Watchdog Timer include:
Eight software-selectable time intervals
Two operating modes: as watchdog or interval timer
Expiration of the time interval in watchdog mode, which generates a sys-
tem reset; or in timer mode, which generates an interrupt request
Safeguards which ensure that writing to the WDT control register is only
possible using a password
Support of ultralow-power using the hold mode
- User’s Guide 1
- Read This First 3
- Notational Conventions 4
- FCC Warning 4
- Contents 10
- Contents 11
- Contents 11
- Figures 13
- Figures 13
- Tables 19
- Examples 20
- Notes, Cautions, and Warnings 21
- 1.1 Features and Capabilities 24
- 1.2 11x Devices 25
- 1.3 11x1 Devices 25
- 1.4 13x Devices 26
- 1.5 14x Devices 26
- Architectural Overview 27
- 2.1 Introduction 28
- 2.2 Central Processing Unit 28
- 2.3 Program Memory 29
- 2.4 Data Memory 29
- 2.5 Operation Control 29
- 2.6 Peripherals 30
- System Resets, Interrupts 31
- 3.1.1 Introduction 32
- Rise Time 33
- Global Interrupt Structure 35
- 3.4 Interrupt Processing 39
- Interrupt Processing 40
- 3.4.2.1 External Interrupts 45
- 3.5 Operating Modes 46
- CPU is disabled 47
- MCLK is disabled 47
- SMCLK and ACLK remain active 47
- CPUOff = 1 49
- SCG0 = 1 49
- SCG1 = 0 49
- 3.5.3 Low-Power Mode 4 (LPM4) 51
- Potential Comment 52
- Chapter 4 53
- 4.1 Introduction 54
- 4.2 Data in the Memory 55
- 4.3 Internal ROM Organization 56
- Internal ROM Organization 57
- 4.4.1 Random Access Memory 58
- Figure 4–6. Register 59
- 4.4.2.1 Word Modules 60
- 4.4.2.2 Byte Modules 61
- 16-Bit CPU 65
- 5.1 CPU Registers 66
- Figure 5–3. Stack Usage 67
- CPU Registers 68
- 5.2 Addressing Modes 71
- 5.2.1 Register Mode 72
- 5.2.2 Indexed Mode 73
- 5.2.3 Symbolic Mode 74
- 5.2.4 Absolute Mode 75
- 5.2.5 Indirect Mode 76
- Addressing Modes 77
- 5.2.7 Immediate Mode 78
- 5.2.8.1 Format-I Instructions 79
- 5.3 Instruction Set Overview 81
- 5.3.3 Conditional Jumps 84
- 5.3.5 Miscellaneous 86
- 5.4 Instruction Map 87
- Hardware Multiplier 89
- 16-Bit Hardware Multiplier 91
- Hardware Multiplier Operation 92
- Hardware Multiplier Registers 97
- Basic Clock Module 101
- 7.1 Basic Clock Module 102
- 7.2 LFXT1 and XT2 Oscillators 104
- 7.2.2 XT2 Oscillator 105
- LFXT1 and XT2 Oscillators 106
- Figure 7–10. DCO Schematic 110
- System Resets, Interrupts and 114
- Operating Modes 114
- Mode for MCLK 117
- LFXT1CLK for Clock MCLK 117
- Digital I/O Configuration 121
- 8.1 Introduction 122
- 8.2 Ports P1, P2 123
- Table 8–1.Port P1 Registers 124
- Table 8–2.Port P2 Registers 124
- Ports P1, P2 125
- 8.3 Ports P3, P4, P5, P6 129
- 8.3.1.1 Input Registers 130
- 8.3.1.2 Output Registers 130
- 8.3.1.3 Direction Registers 130
- 8.3.2 Port P3–P6 Schematic 131
- Watchdog Timer 133
- 9.1 The Watchdog Timer 134
- Table 9–1.WDTCNT Taps 135
- Figure 9–3. Reading WDTCTL 136
- Figure 9–4. Writing to WDTCTL 136
- 9.1.3.1 Watchdog Mode 137
- 9.1.3.2 Timer Mode 138
- 9.1.3.4 Software Example 139
- Chapter 10 141
- 10.1 Introduction 142
- Introduction 143
- 10.2 Timer_A Operation 144
- Timer_A Operation 145
- 10.2.3 Starting the Timer 146
- 10.3 Timer Modes 147
- 10.3.2.1 Timer in Up Mode 148
- Figure 10–9. Timer 149
- Continuous Mode 149
- 10.3.4 Timer—Up/Down Mode 150
- Timer Modes 151
- Figure 10–16. Altering CCR0 152
- Timer in Up/Down Mode 152
- 10.4 Capture/Compare Blocks 153
- Figure 10–19. Capture Signal 155
- Figure 10–20. Capture Cycle 156
- Capture Initiated by Software 157
- 10.5 The Output Unit 159
- 10.5.2 Output Control Block 161
- 10.5.3 Output Examples 162
- 10.6 Timer_A Registers 164
- Table 10–4.Mode Control 165
- Figure 10–28. TAR Register 166
- Timer_A Registers 167
- 10.7 Timer_A UART 173
- Timer_A UART 174
- Chapter 11 177
- 11.1 Introduction 178
- 11.2 Timer_B Operation 181
- Table 11–1. Timer Modes 182
- 11.2.4 Starting the Timer 183
- 11.3 Timer Modes 184
- Immediate Mode for TBCL0 185
- 11.3.3 Timer—Continuous Mode 186
- 11.3.4 Timer—Up/Down Mode 188
- 11.4 Capture/Compare Blocks 191
- Figure 11–19.Capture Signal 192
- Figure 11–20.Capture Cycle 193
- 11.5 The Output Unit 199
- 11.5.2 Output Control Block 201
- 11.5.3 Output Examples 202
- 11.6 Timer_B Registers 205
- Table 11–5. Mode Control 206
- Timer_B Registers 207
- Figure 11–28.TBR Register 208
- 11.6.4.5 Timing Limits 216
- Chapter 12 217
- USART Peripheral Interface 218
- 12.3 Asynchronous Operation 220
- Asynchronous Operation 221
- Example 12–1. 4800 Baud 222
- Example 12–2. 19,200 Baud 222
- Figure 12–7. Idle 223
- Line Multiprocessor Format 223
- Figure 12–11.Address 226
- Bit Multiprocessor Format 226
- SPI Mode 231
- Control and Status Registers 232
- Figure 12–23. Receive 238
- Start Conditions 238
- Figure 12–24. Receive 239
- 12.7 Baud Rate Considerations 241
- Baud Rate Considerations 242
- 12.7.3 Synchronization Error 244
- Chapter 13 247
- 13.2.1 SPI Mode Features 249
- 13.3 Synchronous Operation 250
- Synchronous Operation 251
- 13.3.1 Master SPI Mode 253
- 13.3.2 Slave SPI Mode 254
- 13.5.1 USART Control Register 262
- Comparator_A 267
- 14.1 Comparator_A Overview 268
- 14.2 Comparator_A Description 269
- Comparator_A Description 270
- Comparator_A in Applications 275
- With Applied Analog Signals 276
- This example uses the 0.25×V 281
- Chapter 15 291
- 15.1 Introduction 292
- Sampling 293
- 15.2.1 ADC Core 294
- 15.2.2 Reference 295
- 15.3.1 Analog Multiplexer 296
- 15.4 Conversion Memory 298
- 15.5 Conversion Modes 299
- Conversion Modes 300
- 15.5.6 Power Down 310
- 12–bit S A R 312
- 15.7.3 Sampling Modes 314
- 15.7.3.2 Extended-Sample Mode 316
- 15.8 ADC12 Control Registers 320
- ADC12 Control Registers 321
- ADC12 Interrupt Vector 322
- Register ADC12IV 322
- ADC12IEN.x 327
- Note: Basic Clock System 330
- CPU clock MCLK 330
- Peripheral File Map 333
- A.1 Overview 334
- A.3 Digital I/O, Byte Access 335
- Only modifiable when ENC=0 342
- Watchdog/Timer, Word Access 343
- Instruction Set Description 351
- B.1 Instruction Set Overview 352
- Instruction Set Overview 353
- B.1.1 Instruction Formats 354
- B.1.3 Emulated Instructions 356
- Instruction Set Description 359
- Clear carry bit 369
- Clear negative bit 370
- Decrement destination 375
- Figure B–4.Decrement Overlap 376
- ] Increment destination 380
- Jump if greater or equal 385
- Jump if less 386
- Jump unconditionally 387
- Jump if negative 388
- No operation 392
- Rotate left arithmetically 397
- Rotate left through carry 398
- Flash Memory 413
- C.1 Flash Memory Organization 414
- Simultaneously 415
- Flash Memory Organization 416
- Figure C–4 417
- FUNCTION PERFORMED 420
- CLR &0F012h 421
- C.5.1 Flash Memory Protection 434
- Execution Outside this Module 435
- Outside This Flash Module 438
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