97
CHAPTER 8 INTERRUPTS
8.1.3
Nested Interrupts
You can set different interrupt levels for two or more interrupt requests from peripheral
resources in the interrupt level setting registers (ILR0 to ILR5) to process the nested
interrupts.
■
Nested Interrupts
If an interrupt request of higher-priority interrupt level occurs while an interrupt service routine is being
executed, the CPU halts processing of the current interrupt and accepts the higher-priority interrupt request.
The interrupt level can be set to 0 to 3. If it is set to 3, the CPU will accept no interrupt request.
[Example: Nested interrupts]
To assign higher priority to external interrupts over timer interrupts as an example of processing nested-
interrupts, set the timer interrupt and external interrupt levels to 2 and 1, respectively. If an external
interrupt occurs while a timer interrupt is being processed with these settings in use, the interrupts are
processed as shown in Figure 8.1-3.
Figure 8.1-3 Example of Processing Nested Interrupts
•
While a timer interrupt is being processed, the interrupt level bits in the condition code register (CCR:
IL1, IL0) hold the same value as that of the interrupt level setting registers (ILR0 to ILR5)
corresponding to the current timer interrupt (level 2 in this example). If an interrupt request with a
higher-priority interrupt level (level 1 in the example) occurs, the higher-priority interrupt is processed
preferentially.
•
To temporarily disable nested interrupt processing while a timer interrupt is being processed, set the
interrupt enable flag in the condition code register to disable interrupts (CCR:I = 0) or set the interrupt
level bits (CCR: IL1, IL0) to "00
B
".
•
Executing the interrupt return instruction (RETI) after interrupt processing is completed restores the
program counter (PC) and program status (PS) values saved in a stack and resumes the processing of the
interrupted program.
Restoring the program status (PS) also restores the condition code register (CCR) to its value existing
prior to the interrupt.
(6) Process timer interrupt.
(7) Return from timer interrupt.
(3) External interrupt
occurs.
(4)
Process external interrupt.
(5)
Return from external interrupt.
Timer Interrupt Processing
Main Program
External Interrupt Processing
Interrupt level 2
(CCR:IL1,IL0=10
B
)
Initialize peripheral (1)
resources.
Timer interrupt occurs. (2)
Resume main program. (8)
Resume
Interrupt level 1
(CCR:IL1,IL0=01
B
)
Suspend
Summary of Contents for F2 MC-8FX Family
Page 2: ......
Page 4: ......
Page 34: ...20 CHAPTER 1 DESCRIPTION ...
Page 38: ...24 CHAPTER 2 HANDLING DEVICES ...
Page 39: ...25 CHAPTER 3 MEMORY SPACE This chapter describes memory space 3 1 Memory Space 3 2 Memory Map ...
Page 56: ...42 CHAPTER 5 CPU ...
Page 73: ...59 CHAPTER 6 CLOCK CONTROLLER ...
Page 96: ...82 CHAPTER 6 CLOCK CONTROLLER ...
Page 104: ...90 CHAPTER 7 RESET ...
Page 105: ...91 CHAPTER 8 INTERRUPTS This chapter explains the interrupts 8 1 Interrupts ...
Page 174: ...160 CHAPTER 10 TIMEBASE TIMER ...
Page 184: ...170 CHAPTER 10 TIMEBASE TIMER ...
Page 218: ...204 CHAPTER 13 WATCH PRESCALER ...
Page 257: ...243 CHAPTER 16 8 16 BIT COMPOSITE TIMER ...
Page 261: ...247 CHAPTER 16 8 16 BIT COMPOSITE TIMER ...
Page 288: ...274 CHAPTER 16 8 16 BIT COMPOSITE TIMER ...
Page 301: ...287 CHAPTER 17 16 BIT PPG TIMER ...
Page 316: ...302 CHAPTER 17 16 BIT PPG TIMER ...
Page 382: ...368 CHAPTER 21 UART SIO DEDICATED BAUD RATE GENERATOR ...
Page 390: ...376 CHAPTER 22 I2C ...
Page 395: ...381 CHAPTER 22 I2C ...
Page 399: ...385 CHAPTER 22 I2C ...
Page 430: ...416 CHAPTER 23 10 BIT A D CONVERTER ...
Page 476: ...462 CHAPTER 24 LCD CONTROLLER ...
Page 482: ...468 CHAPTER 25 LOW VOLTAGE DETECTION RESET CIRCUIT ...
Page 494: ...480 CHAPTER 26 CLOCK SUPERVISOR ...
Page 507: ...493 CHAPTER 27 REAL TIME CLOCK ...
Page 523: ...509 CHAPTER 27 REAL TIME CLOCK ...
Page 532: ...518 CHAPTER 27 REAL TIME CLOCK ...
Page 536: ...522 CHAPTER 28 256 KBIT FLASH MEMORY ...
Page 554: ...540 CHAPTER 28 256 KBIT FLASH MEMORY ...
Page 564: ...550 CHAPTER 29 EXAMPLE OF SERIAL PROGRAMMING CONNECTION ...
Page 595: ...581 INDEX INDEX The index follows on the next page This is listed in alphabetic order ...
Page 596: ...582 INDEX Index ...
Page 597: ...583 INDEX ...
Page 600: ...586 Pin Function Index ...
Page 602: ......