Maxim-integrated MAXQ7666 Manual de usuario Pagina 214
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5.3.5 External Crystal-Fail Detection and Automatic Switchover
The MAXQ7665/MAXQ7666 have a high-frequency oscillator-fail detection circuit. An automatic clock switchover from crystal to
7.6MHz RC oscillator is forced if:
• XT = 1 (external crystal is selected as the system clock source).
• XHFRY = 1 (high-frequency oscillator warmup is complete).
• A clock failure (high-frequency source drops below 30kHz) is detected.
When the above condition has been detected, the clock circuitry will:
• Enable the internal 7.6MHz RC oscillator immediately (RCE forced to 1).
• Switch the system clock source from external to internal (XT forced to 0).
• Set the high-frequency crystal failure interrupt flag to 1 (HFFINT = 1).
The 7.6MHz RC oscillator system clock should be ready after a four-cycle delay. This switchover remains in effect until software recon-
figures the clock structure. A crystal failure interrupt is generated if the high-frequency oscillator failure interrupt is enabled (HFFIE =
1). Also, for the interrupt to be acknowledged by the microcontroller interrupt logic, the interrupt request must also be enabled by the
IGE bit in the IC register and IM5 mask in the IMR peripheral register. Figure 5-7 illustrates the external crystal-fail detection and auto-
matic clock switchover flow.
EXTERNAL CRYSTAL FAIL
DETECTION AND AUTOMATIC SWITCHOVER
YES
*NOTE: TRIGGERED WHEN THE HIGH-FREQUENCY
OSCILLATOR DROPS BELOW 30kHz.
**NOTE: INTERRUPT IS GENERATED IF HFFIE, IGE,
AND IM5 ARE SET TO LOGIC 1.
DONE
HIGH-FREQ OSCILLATOR
SELECTED AND STABLE
(XT = 1, XHFRY = 1)
AUTOMATIC SWITCH TO
INTERNAL RC OSCILLATOR
(RCE = 1, XT = 0)
SET HIGH-FREQ FAILURE FLAG
(HFFINT = 1)**
HF OSCILLATOR
FAIL? *
(XHFRY = 0)
NO
Figure 5-7. External Crystal-Fail Detection
MAXQ7665/MAXQ7666 User’s Guide
5-17
Maxim Integrated
- Functional Diagrams 1
- 1.1 Overview 7
- 1.1.2 Instruction Set 8
- 1.1.4 Register Space 8
- 1.2 Architecture 9
- 1.2.1 Instruction Decoding 10
- 1.2.2 Register Space 11
- 1.2.3 Memory Organization 13
- 1.2.3.2 Utility ROM 16
- 1.2.3.3 Data Memory 16
- 1.2.3.4 Stack Memory 17
- 1.2.3.7 Data Alignment 19
- CDA0 = 1 21
- 1.2.4 Interrupts 25
- 1.3 Programming 31
- 1.3.6.1 Sign Flag 37
- 1.3.6.2 Zero Flag 38
- 1.3.6.3 Equals Flag 38
- 1.3.6.4 Carry Flag 38
- 1.3.6.5 Overflow Flag 39
- 1.3.7.2 Unconditional Jumps 39
- 1.3.7.3 Conditional Jumps 40
- 1.3.7.4 Calling Subroutines 40
- 1.3.7.5 Looping Operations 40
- 1.3.8 Handling Interrupts 41
- 1.3.9 Accessing the Stack 42
- 1.3.10 Accessing Data Memory 43
- 1.4.19 General Register (GR) 59
- 2.1 Architecture 75
- 2.3 Supply Configuration 83
- 2.4 Linear Regulator 84
- 2.5 Power-On Reset 84
- 2.5.1 Power-Up Counter 85
- 2.5.3 Reset Output 87
- 2.7 Reset Mode 89
- 2.7.2 External Reset 90
- 2.7.3 Internal System Reset 90
- SECTION 3: ANALOG I/O MODULE 91
- 3.1.1 Analog I/O Pins 96
- Register Name: ACNT 98
- ADCMX2 ADCMX1 FUNCTION 99
- 1 1 Reserved 99
- Maxim Integrated 100
- Section 5 104
- Section 2 104
- Section 3.3.6 107
- Section 3.4 107
- Table 3-2. ADC Signals 108
- Section 3.3.10 110
- 3.3.4 Unipolar/Bipolar 111
- 3.3.5 Transfer Function 112
- Section 3.3.3 115
- Section 3.3.5 115
- 3.3.7 Analog Input Protection 116
- 3.3.8 ADC Clock 117
- 3.3.9 Auto Shutdown Mode 117
- 3.3.11 ADC Interrupts 122
- 3.3.12 Using the ADC 123
- 3.4 Temperature Sensor 124
- Sections 15 125
- TEMPERATURE (°C) 126
- Section 3.4.2 127
- Table 3-12. DAC Signals 128
- 3.5.4 DAC Power-Down 130
- 3.5.5 Using the DAC 130
- LIST OF FIGURES 133
- LIST OF TABLES 133
- 4.1 Architecture 134
- 4.2 CAN Controller Registers 136
- 4.3 CAN Operations 177
- 4.3.1.2 Remote Frame 180
- 4.3.1.3 Error Frame 181
- 4.3.1.4 Overload Frame 181
- 4.5 External Pins 182
- 4.7 CAN Interrupts 183
- 4.8.1 Message Center 15 185
- 4.9.2 Receiving Data Messages 186
- 4.15 Bit Timing 194
- 4.16 CAN Bus Activity 197
- 5.1 Architecture 200
- Section 3 204
- 76543210 205
- Reset 0 0 1 0 0 0 0 1 205
- Access rw r r rw rw rw rw rw 205
- 5.3 System Clock Generation 209
- 5.4 Watchdog Timer 215
- 5.5 Power Management Mode 217
- 5.5.2 Switchback Mode 218
- 5.5.3 Stop Mode 218
- SECTION 6: SERIAL I/O MODULE 219
- 6.1.1 UART Pins 223
- 6.2 UART Registers 223
- Serial Mode Definition 224
- — — — — — — — 226
- 6.3 Modes of Operation 227
- 6.3.3 UART Mode 2 230
- 6.3.4 UART Mode 3 230
- 6.4 Baud-Rate Generation 233
- 6.4.4 Baud-Clock Generator 234
- 6.5 Framing Error Detection 235
- 7.1 Architecture 238
- Compare Mode: 244
- Capture Mode: 244
- 7.2.3 Type 2 Reload Registers 248
- 7.3.3 16-Bit Counter 255
- 7.3.4 Dual 8-Bit Timers 256
- 7.4.3 Measure Period 259
- 8.1 Architecture 264
- 8.1.1 Port Pins 265
- 8.2 Port Registers 265
- 8.3 GPIO Operation 271
- 8.3.4 Port Pin Examples 273
- 9.1 Architecture 276
- 9.1.1 SPI Pins 277
- 9.2 SPI Peripheral Registers 277
- 9.3 SPI Operation 282
- 9.3.2 SPI Slave Operation 283
- 9.3.3 SPI Transfer Formats 284
- 9.4 SPI Transfer Baud Rates 285
- 9.5 SPI System Errors 285
- 9.6 SPI Interrupts 286
- 10.1 TAP Overview 289
- 10.2 Architecture 289
- 10.2.1 TAP Pins 290
- 10.3 TAP Interface Control 291
- 10.4 TAP Controller Operation 292
- 10.4.2 Run-Test-Idle 293
- 10.4.3 IR-Scan Sequence 293
- 10.4.5 Communication via TAP 294
- 11.1 Architecture 299
- Section 12 303
- Section 10 305
- Section 1 305
- 11.3 Debug Engine Operation 306
- 11.3.2 Breakpoint Registers 308
- 11.3.3 Using Breakpoints 310
- 11.3.4 Debug Mode 311
- 11.3.5 Debug Mode Commands 311
- 11.3.8 Return 313
- 12.1 Bootstrap-Loader Mode 317
- Section 11 318
- Section 12.5 320
- 12.5 JTAG Bootloader Protocol 321
- 13.6 Operand Count Selection 335
- 13.8 Accessing the Multiplier 336
- Acc.<b> 343
- 1000 1010 0001 1010 345
- 1101 1010 0010 1010 346
- 0011 1100 ssss ssss 349
- 0111 1100 ssss ssss 349
- 1111 1010 bbbb 1010 352
- 1101 1010 0000 1010 353
- 1110 1010 bbbb 1010 353
- 1101 1010 0001 1010 354
- 1ddd dddd 0bbb 0111 354
- 1ddd dddd 1bbb 0111 354
- 1000 1010 1001 1010 355
- .<b> 356
- 1110 1100 0000 1101 359
- 1001 1100 0000 1101 359
- 1101 1100 0000 1101 359
- 1100 1100 0000 1101 359
- 1000 1100 1000 1101 360
- 1010 1100 1000 1101 360
- 1110 1100 1000 1101 360
- 1001 1100 1000 1101 361
- 1101 1100 1000 1101 361
- 1100 1100 1000 1101 361
- 1000 1010 0100 1010 362
- 1000 1010 0101 1010 362
- 1000 1010 1100 1010 363
- 1000 1010 1101 1010 363
- 1000 1010 0010 1010 364
- 1000 1010 0011 1010 364
- 1000 1010 0110 1010 364
- 1000 1010 1010 1010 365
- 1000 1010 1111 1010 365
- 1000 1010 1110 1010 366
- 1000 1010 1011 1010 366
- 1000 1010 0111 1010 368
- 1000 1010 1000 1010 368
- 1011 1010 bbbb 1010 369
- WITH TYPE A FLASH) 371
- 15.2 Data Transfer Functions 372
- TYPE F FLASH) 378
- 16.2 Data Transfer Functions 383
- REVISION HISTORY 386
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