7751 Group User’s Manual
INTERRUPTS
4–18
4.8 Return from interrupt routine
When the RTI instruction is executed at the end of the interrupt routine, the contents of the program bank
register (PG), program counter (PC), and processor status register (PS) immediately before performing the
INTACK sequence, which were saved to the stack area, are automatically restored, and control returns to
the routine executed before the acceptance of interrupt request and processing is resumed from it left off.
For any register that is saved by software in the interrupt routine, restore it with the same data length and
same register length as it was saved by using the PUL instruction and others before executing the RTI
instruction.
4.9 Multiple interrupts
When a branch is made to the interrupt routine, the microcomputer becomes the following situation:
•Interrupt disable flag (I) = “1” (interrupts disabled)
•Interrupt request bit of the accepted interrupt = “0”
•Processor interrupt priority level (IPL) = interrupt priority level of the accepted interrupt
Accordingly, as long as the IPL remains unchanged, the microcomputer can accept the interrupt request that
has higher priority than the interrupt request being executed now by clearing the interrupt disable flag (I)
to “0” in the interrupt routine. This is multiple interrupts.
Figure 4.9.1 shows the multiple interrupt mechanism.
The interrupt requests that have not been accepted owing to their low priority levels are retained. When the
RTI instruction is executed, the interrupt priority level of the routine that the microcomputer was executing
before accepting the interrupt request is restored to the IPL. Therefore, one of the interrupt requests being
retained is accepted when the following condition is satisfied at next detection of interrupt priority level:
Interrupt priority level of interrupt request being retained > Processor interrupt priority level (IPL)
4.8 Return from interrupt routine 4.9 Multiple interrupts
Summary of Contents for 7700 FAMILY
Page 2: ...MITSUBISHI 16 BIT SINGLE CHIP MICROCOMPUTER 7700 FAMILY 7751 SERIES 7751 Group User s Manual...
Page 11: ...Table of Contents viii 7751 Group User s Manual MEMORANDUM...
Page 157: ...TIMER B 6 28 7751 Group User s Manual 6 5 Pulse period pulse width measurement mode MEMORANDUM...
Page 245: ...7751 Group User s Manual 8 36 A D CONVERTER Precautions when using A D converter MEMORANDUM...
Page 265: ...7751 Group User s Manual WAIT MODE 11 6 11 3 Precautions for Wait mode MEMORANDUM...
Page 289: ...CONNECTION WITH EXTERNAL DEVICES 12 4 Hold function 7751 Group User s Manual 12 24 MEMORANDUM...
Page 290: ...CHAPTER 13 RESET 13 1 Hardware reset 13 2 Software reset...
Page 302: ...CHAPTER 14 CLOCK GENERATING CIRCUIT 14 1 Oscillation circuit example 14 2 Clock...
Page 307: ...CLOCK GENERATING CIRCUIT 7751 Group User s Manual 14 6 14 2 Clock MEMORANDUM...
Page 360: ...CHAPTER 16 STANDARD CHARACTERISTICS 16 1 Standard characteristics...
Page 366: ...CHAPTER 17 APPLICATIONS 17 1 Memory expansion...
Page 405: ...APPLICATIONS 7751 Group User s Manual 17 40 17 1 Memory expansion MEMORANDUM...
Page 406: ...CHAPTER 18 PROM VERSION 18 1 EPROM mode 18 2 Usage precaution...
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Page 418: ...CHAPTER 19 FLASH MEMORY VERSION 19 1 Parallel input output mode 19 2 Serial input output mode...
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Page 536: ...GLOSSARY...
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