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The Watchdog Timer
9-3
Watchdog Timer
9.1.1 Watchdog Timer Register
The watchdog-timer counter (WDTCNT) is a 16-bit up-counter that is not
directly accessible by software. The WDTCNT is controlled through the
watchdog-timer control register (WDTCTL), shown in Figure 9–2, which is a
16-bit read/write register located at the low byte of word address 0120h. Any
read or write access must be done using word instructions with no suffix or
.w
suffix. In both operating modes (watchdog or timer), it is only possible to write
to WDTCTL using the correct password.
Figure 9–2. Watchdog Timer Control Register
HOLD
70
rw–0
WDTCTL
0120h
NMINMIES TMSEL SSEL IS1 IS0CNTCL
rw–0 rw–0 rw–0 r0(w) rw–0 rw–0 rw–0
15 8
069h
05Ah
WDTCTL
read
WDTCTL
write
Bits 0, 1: Bits IS0 and IS1 select one of four taps from the WDTCNT, as
described in Table 9–1. Assuming f
crystal
= 32,768 Hz and
f
System
= 1 MHz, the following intervals are possible:
Table 9–1.WDTCNT Taps
SSEL IS1 IS0 Interval [ms]
0 1 1 0.064 t
SMCLK
× 2
6
0 1 0 0.5 t
SMCLK
× 2
9
1 1 1 1.9 t
ACLK
× 2
6
0018t
SMCLK
× 2
13
1 1 0 16.0 t
ACLK
× 2
9
00032t
SMCLK
× 2
15
<– Value after PUC (reset)
1 0 1 250 t
ACLK
× 2
13
1 0 0 1000 t
ACLK
× 2
15
Bit 2: The SSEL bit selects the clock source for WDTCNT.
SSEL = 0: WDTCNT is clocked by SMCLK .
SSEL = 1: WDTCNT is clocked by ACLK.
Bit 3: Counter clear bit. In both operating modes, writing a 1 to this bit
restarts the WDTCNT at 00000h. The value read is not defined.
Bit 4: The TMSEL bit selects the operating mode: watchdog or timer.
TMSEL = 0: Watchdog mode
TMSEL = 1: Interval-timer 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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